Battery Capacity, Longevity, and Manufacturer Reserves

[WARPed1701D]

After a ton of searching and reading I've concluded that battery capacity, longevity, and what we can do to preserve them has been the topic of many conversation on this forum. It is understandable too. After all the ability of the battery to safely deliver in an array of circumstances and environmental conditions makes the difference between a safe ride and a face-plant. Replacement power packs also seem to cost about the same as half of a new wheel! Ouch! I've been concentrating on what I can do to preserve the capacity of the battery in my newly ordered Inmotion V8. For the type of wheel the V8 has a relatively low capacity and so a restricted range compared to say the KS 16S but wins in the area of waistline and weight.

I'm loath to start another thread when there are so many already but I have a few questions that appear to have, so far, been unanswered.

Conventional wisdom on the forum derived through discussion and a heavy reliance on the information from Battery University (batteryuniversity.com hereafter referred to as BU) is that if you can get away with only charging to 80% and performing 50% discharge you will return you the best bang for your battery buck with regards to increasing the number of charge cycles by 4 or 5 times. BU reports that EV's such as the Nissan Leaf and Tesla models do this by charging to 80% capacity for a "full tank" and considering 30% to be an "empty tank".  This maximizes charge cycles  of the hugely expensive batteries and then by dynamically increasing this usage range beyond the initial 50% limit as the battery ages the vehicle is able maintain mileage specs over a number of years.

BU considers a full charge discharge cycle to take a single cell's voltage from 3.0V (empty) to 4.2V(full). So following their suggestion of say an 80% capacity charge and only 50% usage to 30% capacity suggests a charged cell voltage of 3.96V and a discharged cell voltage as 3.36V. This is where I want help. The thing is, in the interest of safety I understand most EUC manufacturers artificially increase the "empty" voltage of a cell above 3.0V. From information I read on this forum from Jason Inmotion's cutoff voltage is 68V (over a 20 series 2 parallel setup) giving an empty cell voltage of 3.4V. With this in mind, ignoring any safety aspects of potential for restricted current delivery at low voltages, to achieve the best balance of capacity and longevity from my V8 battery I should charge to 80% (according to a 3rd party too such as the Charge Doctor, not the V8's battery indicator) cell capacity (3.96V) and then discharge until the V8 considers the tank dry (actual 3.4V) which in reality BU would consider still to be 33% actual cell capacity. Thus I consumed only 47% capacity. Do you agree with this conclusion?

If I were to charge to 80% and discharge to 30% following the Inmotion battery indicator only for both levels then I'm guessing I'd actually be charging to 4.04V (80% of the 3.4V to 4.2V range, 86% of actual 3.0 to 4.2V cell range) and discharging to 3.64V (30% of the 3.4V to 4.2V range, 53% of actual 3.0 to 4.2V cell range) meaning I actually only get to use 33% of the real battery capacity vs the 50% I think I'm using.

In another post on the forum in Jason's initial review of the V8 prototype he says that the V8 remained responsive and performed well right down to empty. So, if Inmotion keeps so much power in reserve and the wheel appears solid even at lower voltages I'm thinking of doing the 80% charge via Charge Doctor and drain to near flat as my usual routine to hit that balance of range and longevity (unless it is cold, then I’ll leave extra in the tank).

What are your thoughts, first on my initial battery conclusions and then on my consideration to use the battery down to Inmotion’s definition of empty? I appreciate your input.

P.S. If we can keep the discussion relatively layman that would be awesome!
 

[The Fat Unicyclist]

I've always found this interesting... And my opinion is that the correct answers depend on how you define longevity - is that solely a period of time? 

Using really simplified logic (even though it may end up ruining my argument)... if I actively manage my battery - charging to ~80% / riding to ~50% - then I am using a but over a quarter of the full charge. Now that may mean my battery lasts for times longer, but when I went to school, 1/4 × 4 = 1

So this may occur over a longer period of time, but wouldn't the overall riding distance be about the same? 

In this case,  should "longevity" also consider distance? 

[WARPed1701D]

Longevity IMO is largest possible power output for the device over it's usable life (ergo miles) while remaining practical.

Indeed if using 1/4 of the battery resulted only resulted in 4 times more charges then you would not be getting anywhere, however I believe the suggestion at BU is to charge to 80% and drain to 30% and it will give you around 4 or more times the number of cycles at the cost of only getting 50% possible power from your batter per cycle. If you can do that realistically and practically then the net result is at least twice the usable power (miles) over the battery life.

My point with this post though is that our definition of empty is artificially inflated for safety by the manufacturer (a good thing) and what we think is 50% capacity usage is actually more like 33% in real terms. It explains why energy in during charging (as measured by a Charge Doctor) can seem oddly low for an apparently empty battery. We actually only have 66% of the battery's full potential available to us and when we limit our minimum charge level to 30% we reduce the available charge even further.

Worst case scenario: Assuming I charged to 80% as measured by charge doctor and discharge to 30% as measured by the wheel actual capacity used drops to just 27%.

This discussion also lends itself to storing our wheels. Ideally if you aren't storing for more than a year and the battery isn't to old with high self discharge you should store a Li-Ion battery at about 30% real world capacity as measured from 3.0V. In Inmotion's case this actually means you should store it completely empty as measured by the wheel itself as this is actually 33% real world charge. Charging to 30% as measured by the wheel means you end up storing the battery at over 50% real world capacity. Still not bad and certainly good for very long storage or older batteries that self discharge higher but not as good for shorter term storage, or in warmer conditions.

[US69]

27 minutes ago, The Fat Unicyclist said:

I've always found this interesting... And my opinion is that the correct answers depend on how you define longevity - is that solely a period of time? 

Using really simplified logic (even though it may end up ruining my argument)... if I actively manage my battery - charging to ~80% / riding to ~50% - then I am using a but over a quarter of the full charge. Now that may mean my battery lasts for times longer, but when I went to school, 1/4 × 4 = 1

So this may occur over a longer period of time, but wouldn't the overall riding distance be about the same? 

In this case,  should "longevity" also consider distance? 

@The Fat Unicyclist i think you got something wrong:

A full chargecycle, which is always mentioned on longevity, means a charge from 0-100%....

meaning, that when you charged you unicycle for example 4! times from 50-80%...you are on 1.2 chargecycles....so just a bit over One full charge cycle!

so, my thoughts on this:

Yes, @WARPed1701D getting your wheel batterie allways to stay between 20-80% charging will double the lifetime, so will give you 1000 full cycles instead of only 500(while this numbers are only rough assumptions)!

And yes, to have it between 50-80% can have another impact on longevity...maybe it 4 times the assumpted 500 FULL cycles to 2000....

But as i am driving now a bit , my 2 (at the moment) main wheels have about 2X1500km on the clock....my view is you are worrying a bit to much. Our batteries are allways announced to have 500-1000 FULL cycles, and at that time, the batteries are just getting weaker, not dead. lets say thats to optimistic and only think about 300 full cycles.....

That are sooo much miles or km an soooo much time..till you reach even that 300 FULL cycles, that in the meantime, you will perhaps have 2 other nice wheels, or get marriaged or divorced or some more children ;-)

Not that you are not right, you researched everything correct! :-) But thats taking the fun out of the game, to allways check if my batterie is between 50-80%.....and also think about special producers announcing then.

i am personally on my 2 over 1100wh wheels, trying to charge not over 90%....and just do a full charge all ten cycles...

And otherwise just dont drive under 20%....but i seldom reach this, mostly when reaching 30-40% my EUC goes to the powerplug, but thats more because of safety concerns, than from batterie longevity!

So far that worked nicely, like said both momentary wheels have 1500km, me and the charge doctor feel/see no loose of Watthours.

[WARPed1701D]

 Thanks for the reply KingSong69.

I couldn't find the definition of a cycle on BU's site. I assumed a cycle to be from the point of the given discharge until full again. Ergo charges of 50% represented 2 cycles rather than 1 of 100% total (2 x 50%). Either way it is an increase.

You are right of course to enjoy the wheel and not stress about it. I guess I'm raising this from several angles. If I've worked it all out correctly then (safety of the wheel aside) draining my V8 to empty actually still leaves 33% capacity in the cells and a voltage of 3.4 volts. People assume draining to empty is a huge stress on the cells but in our case of an artificially inflated empty level that is not so. Riding to empty should be of no detriment to the cell and as long as your wheel is proven reliable and safe at low charge values you should be OK to use all your power up.

In the case of my V8 which doesn't have the largest range it may mean I can happily (although gently) go another 5 or 6 miles more than I would have if I was worried about stressing the cell with a deep discharge.

[US69]

11 minutes ago, WARPed1701D said:

 Thanks for the reply KingSong69.

I couldn't find the definition of a cycle on BU's site. I assumed a cycle to be from the point of the given discharge until full again. Ergo charges of 50% represented 2 cycles rather than 1 of 100% total (2 x 50%). Either way it is an increase.

You are right of course to enjoy the wheel and not stress about it. I guess I'm raising this from several angles. If I've worked it all out correctly then (safety of the wheel aside) draining my V8 to empty actually still leaves 33% capacity in the cells and a voltage of 3.4 volts. People assume draining to empty is a huge stress on the cells but in our case of an artificially inflated empty level that is not so. Riding to empty should be of no detriment to the cell and as long as your wheel is proven reliable and safe at low charge values you should be OK to use all your power up.

In the case of my V8 which doesn't have the largest range it may mean I can happily (although gently) go another 5 or 6 miles more than I would have if I was worried about stressing the cell with a deep discharge.

In the "industrial" 18650 world, most of the batteries are meant to run from -about- 3,3 volt to 4,2 volt.

So i guess your Inmotion 3,4 volt assumption is not completly "correct"....To drain the batterie to 3 volts and mean that a 0% charge...is possible, but not the standard. But...some cells can even be drained to 2,7 or 2,8 volts...so that would lead to take a look at the specific cell which is used in the wheel, and i guess this goes the wrong direction.

From my experiences with batteries i would assume they are in a range from 3,3 to 4,2 volts...that numbers i also know from my vaping gear, which uses the same kind of cells.

 

 

[steve454]

24 minutes ago, WARPed1701D said:

stressing the cell with a deep discharge.

From what I read on this forum, a lot of wheels will not let you stress the cells with deep discharge.  I'm thinking that the battery management systems of most high quality wheels protect the batteries pretty well.  You have good idea to make your batteries last longer by not charging all the way.  But like @KingSong69 said, it will be a long time before the batteries wear out.  Sounds like the V8 has good reserves at low battery.

[WARPed1701D]

51 minutes ago, KingSong69 said:

In the "industrial" 18650 world, most of the batteries are meant to run from -about- 3,3 volt to 4,2 volt.

So i guess your Inmotion 3,4 volt assumption is not completly "correct"....To drain the batterie to 3 volts and mean that a 0% charge...is possible, but not the standard. But...some cells can even be drained to 2,7 or 2,8 volts...so that would lead to take a look at the specific cell which is used in the wheel, and i guess this goes the wrong direction.

From my experiences with batteries i would assume they are in a range from 3,3 to 4,2 volts...that numbers i also know from my vaping gear, which uses the same kind of cells.

 

 

 Fair point. I was using info here...

http://lygte-info.dk/review/batteries2012/LG 18650 MH1 3200mAh (Cyan) UK.html

...for cell performance data,suggesting that a 3.0V discharge was a good end point  for these cells.

[WARPed1701D]

30 minutes ago, steve454 said:

From what I read on this forum, a lot of wheels will not let you stress the cells with deep discharge.  I'm thinking that the battery management systems of most high quality wheels protect the batteries pretty well.  You have good idea to make your batteries last longer by not charging all the way.  But like @KingSong69 said, it will be a long time before the batteries wear out.  Sounds like the V8 has good reserves at low battery.

 My conclusion precisely, although high quality  are the key words there. I have read many other posts though where people are concerned about running the charge low for reasons of battery damage. As it seems I'm on the right track with my assumptions presented here i hope it helps others.

Safety first though. Wheels with poor battery reserves may have you eating asphalt if you run them too low. I'm glad I found the cut off voltage for Inmotion wheels from a reliable source.

 

[steve454]

13 minutes ago, WARPed1701D said:

Safety first though. Wheels with poor battery reserves may have you eating asphalt if you run them too low.

I agree completely, it's hit and miss with cheap wheels with small batteries. 

[Keith]

@WARPed1701D, just to pick up on an error right at the start of this discussion, I've just trawled through BU to check I'm not in error, at 3.4 volts off-load a Lithium Ion cell has somewhere in the region of 10% capacity left - not 33% as you stated.

You must have picked up figures that were on-load - but how much load?  The problem with voltage versus capacity is that internal cell resistance has significant impact when the cell voltage is low, I.e. The voltage falls off of a cliff below 20% capacity.

So how much capacity you have left at 3.4 volts rather depends upon how much power the wheel was demanding at the time, drive slowly and the voltage will rise and allow more capacity to be taken from the battery. Kingsong used to have low battery set at 55V ( my early wheel still is and it plays havoc with its range) Off load that would be about the right figure, Jason worked with Kingsong to get it lowered to 48 volts (3 V/cell) which improved range significantly and is still not actually that low a voltage under load unless you have a very big multi-parallel cell battery.

@KingSong69's first reply above concurs with my opinion, it's not really worth worrying about that much, use a Charge Doctor when it is convenient to not fully charge (but remember to occasionally do a full charge to maintain cell balance) and don't leave the cells fully charged for long periods of time, but above all don't over worry about it and just use good sense, if you need to go right down to empty to get home you are going to do so aren't you, but don't just keep going for a ride every day until the battery is flat and then charging it.

[WARPed1701D]

46 minutes ago, Keith said:

@WARPed1701D, just to pick up on an error right at the start of this discussion, I've just trawled through BU to check I'm not in error, at 3.4 volts off-load a Lithium Ion cell has somewhere in the region of 10% capacity left - not 33% as you stated.

 

Ok. Thanks for the correction. Do you have links to the BU pages. I'd like to learn more about this. 

[Keith]

8 hours ago, WARPed1701D said:

Do you have links to the BU pages. I'd like to learn more about this. 

This is as good a place to start as any: http://batteryuniversity.com/learn/article/lithium_based_batteries. On this page is a graph of voltage against capacity comparing older coke anode batteries to modern graphite anode ones. The older coke anode batteries would have had around 30% capacity at 3.4 volts.

This fits with the LiPo batteries I use somewhat aggressively every weekend in model helicopters/planes. LiPo's are basically soft cased LiIon batteries with pretty much the same electrical characteristics, if, off load, a battery is down to less than 3.5V/cell I will put over 90% charge back into it, if it is way down at 3.0 volts it is only a tiny bit more. In practice I try to fly only down to 3.6V off load if I can. I also notice that batteries taken down below 3.4 volts or so are noticeably warmer when removed from the 'plane.

[WARPed1701D]

Thanks for the link. There are so many articles on that site and I had been concentrating on the ones regarding longevity and discharge. Must have skipped over the generic one until now.

Let me confirm your terms "off-load" and "on-load" voltages.

"On-load" is, I'm guessing, the voltage of the battery with a current draw. And as I understand it a high current draw lowers lower the output voltage which then recovers to the nominal value when the load is removed. Yes? With the highly variable load produced by the wheel motor I'm guessing this value fluctuates to some degree.

Now, "off-load". Do you mean the voltage as soon as the load this removed or after 10 minutes or so for the battery to rest. I understand even a fully depleted but healthy LI-ion battery will recover to near nominal voltage after a few minutes simply due to the electrode's affinity even though there is little capacity left to deliver.

Source of my assumptions: http://batteryuniversity.com/learn/article/discharge_methods

If that is the case then surely the voltage under load is the only reliable gauge of capacity. Yes?

Also I see posts where people report they drain their wheels to empty but then after a short period note that the remaining percentage of charge has increased into the teens or higher. This suggests that remaining capacity as declared by the wheel can be inaccurate at rest when the battery is very low on charge and that reported remaining charge is maybe only measured based on cell voltage?

 

 

[esaj]

Late to this thread, as I'm catching up on posts...

On 6/30/2017 at 5:54 PM, WARPed1701D said:

Let me confirm your terms "off-load" and "on-load" voltages.

"On-load" is, I'm guessing, the voltage of the battery with a current draw. And as I understand it a high current draw lowers lower the output voltage which then recovers to the nominal value when the load is removed. Yes? With the highly variable load produced by the wheel motor I'm guessing this value fluctuates to some degree.

Yes, the voltage varies... When the battery has been discharged further, the voltage starts to drop off faster. I had a voltage meter fixed to my Firewheel at one point, and when the battery pack (16S2P) voltage dropped to somewhere around 53-54V, or around 3.3...3.375V / cell at rest ("off-load"), "on load" it would drop to 50...52V at light loads and down to 46-48V or 2.875...3.0V / cell at high current demand (strong acceleration and/or climbing). The Firewheel seemed to hit the battery warning (where it tilts back, starts to play the warning message and forces you to slow down to stop) at around 2.9V per cell (46.4V for the pack). Also the internal resistance of the cells goes up with temperature, and when they need to push out more current at lower voltage, the cell heats up more, causing higher resistance, which still drops the voltage further under load.

 

Quote

Now, "off-load". Do you mean the voltage as soon as the load this removed or after 10 minutes or so for the battery to rest. I understand even a fully depleted but healthy LI-ion battery will recover to near nominal voltage after a few minutes simply due to the electrode's affinity even though there is little capacity left to deliver.

The cells won't get back to nominal voltage (3.6-3.7V) once more discharged, but they will "regain" some voltage with no or very small load on them for a while. Another real world example is that after hitting the battery warning on the Firewheel, I could let it rest (turned off) for some minutes, and continue riding. Typically the battery warning would first come during a climb or faster acceleration, so it hit the threshold-voltage under higher discharge current, but it could still be ridden a few kilometers more gently, if left to rest for a bit.

 

Quote

Source of my assumptions: http://batteryuniversity.com/learn/article/discharge_methods

If that is the case then surely the voltage under load is the only reliable gauge of capacity. Yes?

Voltage is the thing pretty much, and it seems that's what the wheels look at when measuring the remaining battery, which makes sense. If you look at the discharge curves for cells at different (continuous) discharge currents in places like http://www.dampfakkus.de/ , you'll notice that the cells deliver actually less (milli)amphours when discharged at higher rates. The energy stored in the cells isn't "disappearing", but it's being burned off as heat in the cell internal resistance. The higher the current, the more energy is wasted as heat in the cell itself (even when the internal resistance isn't changing with the temperature).

 

Quote

Also I see posts where people report they drain their wheels to empty but then after a short period note that the remaining percentage of charge has increased into the teens or higher. This suggests that remaining capacity as declared by the wheel can be inaccurate at rest when the battery is very low on charge and that reported remaining charge is maybe only measured based on cell voltage?

 

Like said above, I believe the wheels only look at the battery pack (as a whole) voltage to determine the charge state (of course I have no proof of this, but my empirical data seems to support the conclusion ). The thing is, the voltage will go up somewhat if you leave the wheel to rest for a while, but it's not magically recharging. Letting the wheel to rest and then riding gently will allow you to make a little more way, but after each time the battery warning starts, and you rest it for a little while, you get less and less mileage before the next warning. You're actually "forcing" a more deep discharge on the cells this way, but of course if you're stranded a few km from home, it's a way to get there without having to carry the wheel... done it a couple of times with the Firewheel

Taking care of the battery pack "health" and longevity is good in general, but don't overstress it. Enjoy the wheel, use lower charge when you don't need the full range and occasionally charge it to full just for balancing, even if you don't need the full range ever. The pack will lose capacity over time, even if you just leave it sitting in a shelf in the "correct" storage voltage, but that's just how it is.

[steve454]

I wonder which wheel has the best battery management system, that allows high performance without cutout.  My guess would be IPS or Kingsong followed by Ninebot.  Gotway is high performance, needs a lot of rider skill to stay safe.

[esaj]

40 minutes ago, steve454 said:

I wonder which wheel has the best battery management system, that allows high performance without cutout.  My guess would be IPS or Kingsong followed by Ninebot.  Gotway is high performance, needs a lot of rider skill to stay safe.

Pure guesswork, but IPS might be the "leader" in this, as (at least earlier) they seemed to design the BMSs straight into the mainboards (so it's "purpose-built" exactly for the wheel), whereas all the other manufactures (at least of which I've seen the teardowns/pictures of the boards) seem to use separate BMS-boards in the battery packs. The Firewheel packs held well, despite the fact that they were cycled a good 300-400 or maybe even more times (by estimate) and I probably overcharged them a bit all the time (hot off the charger at full voltage and my trips always start with a few hundred meters of downhill riding, as I live in a top of a hill), and it did let them discharge to <3.0V (under load, in rest the voltage would go back up to around 3.3V / cell). For "allowing high performance without cutout", depending what you actually mean with that, but if you just want high output without cut-outs, that basically means no (or very, very high) output current limit, so Gotway (no discharge protections, which may not be just a good thing) or shunted packs. Of course, as we've seen with Gotways & others, other parts of the mainboard will get destroyed by high enough current, but at least it wasn't the BMS causing the cutout?

I had shunted packs on the Firewheel (which is among the least safe wheels ever, no speed- or current-based tiltbacks, and without shunts, it would just cut out above 28km/h), but those are a double-edged sword, just like the unprotected Gotway packs, if something on the mainboard or wiring short-circuits, the pack won't stop dishing out current and will (eventually) destroy something in the path (if nothing else, the cells will catch fire/explode). I'd like to have protections at least when working with the packs, this is what the Firewheel packs did to my measurement probes after accidental short-circuit (and at this point, the shunt-wire was already cut off, so the BMS did cut the current after the initial spike, the slowish 10A fuse in the multimeter didn't even have enough time to blow):

The red-probe tip was vaporized. Someone else had a pic of their own mishap, where the entire tip was gone, right down to the plastic. That's solid metal, heated to melting/vaporization point at an instant. Most of you have probably seen that picture a gazillion times already, but it's a good reminder of how much power these (relatively) small packs carry.

 

 

[esaj]

To continue on the topic of discharge current, I think something needs to be clarified (although probably mentioned many times in the forums in the past): you'll see discharge currents like 10A or 20A mentioned for specific cells. These are manufacturer recommendations how much current to pull continuously out from the cell at maximum, or risk damaging the cell. Apart from the BMS-protections (the wheels use unprotected cells, there are protected cells with "mini-BMSs" built into the cells, but those aren't good for wheels), there's nothing in the cells themselves to limit the current / cut the power, except the internal resistance and voltage. The 10/20/whatever amps is recommendation, if you short circuit a cell, it will "happily" discharge 100A or whatever, only limited by the resistance of the path the current takes and the voltage of the cell (which will drop during the discharge a bit, but still). Shorting a cell fully charged to 4.2V with 30 milliohm internal resistance over a wire & connections with, say just for an example, 10 milliohms of resistance will cause over 100A of current:

 

[WARPed1701D]

Some awesome information there @esaj Thanks for taking the time.

I guess in my original opening post where I say that, based on the 3.4V shutoff in the Inmotion wheels, there would be maybe 30% charge left in the pack when the wheel showed completely empty I was talking about the reading shown by the wheel at the point of initial tilt-back and shut off when it hit 3.4 V under a moderate load while riding (the 'on load' condition). I wasn't suggesting that there would be 30% charge remaining in the cells if the wheel reported a empty battery 'off load' after it had sat for a while to rest and recover. Getting to that point would, as you mentioned, be difficult as you would have to keep turning the device back on and riding further to enforce a deeper drain and so a lower resting voltage.

I'm not stressing too much about my battery pack but I like to understand how things work, what safeguards are built in already, and what I can do to maximize value and efficiency of my machine without risking my safety or my wheel's mechanical/electrical integrity. Based on these discussions I feel comfortable that I can charge to 80% on the Charge Doctor and discharge to 10% or less (if desired and with careful riding) and not be risking my battery. I'll do checks with the Charge Doctor when I get it to see exactly how much energy goes in after running to these levels but I expect that this kind of discharge cycle will use about 50% battery capacity which is a good amount for pack longevity.

[Rehab1]

2 hours ago, esaj said:

 Most of you have probably seen that picture a gazillion times already, but it's a good reminder of how much power these (relatively) small packs carry.

Before my accident I was not fully aware about the tremendous amount of power stored in the packs! Always treat EUC battery packs with the same degree of caution and respect as you would working with household current! 

 

 

[esaj]

37 minutes ago, Rehab1 said:

Before my accident I was not fully aware about the tremendous amount of power stored in the packs! Always treat EUC battery packs with the same degree of caution and respect as you would working with household current! 

Yes, the packs can be lethally dangerous if mishandled. Of course "mishandling" shouldn't mean pushing the connectors together, like in your case, but even DC-voltage is dangerous at higher levels and "right" conditions. A lithium fire or a pack exploding in your face is not funny, and if high enough current passes through your heart (like from one hand to the other, "conveniently" with your heart in the way), it will stop it. That's not to scare people, but to remind to be careful with these things. They're relatively harmless sitting inside the wheel (as long as not overcharged, overheated, short-circuited or let to discharge to a too low voltage and then recharged), but if you have to open up your wheel, disconnect the battery pack, and at least try to turn the wheel on after disconnecting the pack, or otherwise drain the capacitors on the board so no large voltages are there. Many people have replaced a burnt mainboard or bad battery packs without any trouble, but taking precautions is wise.

[zlymex]

I don't care much about the battery as far as charge/discharge is concerned.

For most of the time, I just plug the charger. No smart switch, no alarm/timer clock, no frequent check, no worrying about whether it is being charged too full.

There are two exceptions when I unplug the charger before fully charged, one is before sleep, the other is lunch break during long distance ride when time is limited.

I believe that 4.2V is the optimum voltage compromised for safety, capacity and longevity for most of 18650 cells, and a quality charger together with the BMS will maintain the cell voltage equal to or slightly below 4.2V even if the charged for infinite time.

There is a chart by Panasonic indicating that there is only minor difference in capacity decay for charge to 4.1V and 4.2V, and only happen after 400 full cycles(page 42, for a particular cell) http://www.embedded-world.eu/fileadmin/user_upload/pdf/batterie2011/Sonnemann_Panasonic.pdf

 As for the discharge, the averaged voltage of my V3s+ will maintain above 3.3V even if the low battery till-back happens for several times, meaning there is still a lot reserve.

What I do care is the unbalance of the battery pack, because of four things:
1. once the unbalance happened, it tends to become more severe.
2. unbalanced pack lessen the total capacity.
3. unbalanced pack(up to certain point) may over-discharge the low-voltage cell/cells at low battery.
4. unbalanced pack(up to certain point) is very difficult to recover because the charge protection circuit will be triggered at early stage of the charge, and cut off the charge current(hence cut off the balancing current) completely.

 I balance charge my EUC by frequently charged to full, and continue charging for 2 house or so.

One thing worth noting is that occasionally charge to 'full' may not functions as balancing the cells at all if that 'full' means the charger's LED has just turned to green. Once the light turns to green, there is still about 0.3A to 1A charge current(depending on maker and normal charge current of the charger), and the average battery voltage is about 4.15V, this normally not enough to invoke the balancing circuit. The balance ICs used now days are mostly BB3A(HY2215, http://www.hycontek.com/en/products-en/3211)that start balancing at 4.20V and stop at 4.19V. 

 

A fully balanced battery pack can be best shown by all the switches(MOSFETs or transistors) are turned on which can be viewed by an IR camera that all the balancing resistors are hot.

[Marty Backe]

I probably don't represent the average rider, but I don't think I'll own any given wheel for more than a couple of years. So I just charge to 100 percent and don't worry about it. I'm more focused on having fun with the wheel. And since I enjoy long rides I'd rather have the additional 10% battery capacity for my longer ride than to extend the life of the batteries.

I did just get a fancy charger from EWheels so I may charge my Monster to only 90%, but only because it has such a huge range that I won't miss that 10% charge.

[WARPed1701D]

3 hours ago, zlymex said:

I don't care much about the battery as far as charge/discharge is concerned.

......<snip>......

 Some great info here about the importance of balancing the pack regularly, side effects of an imbalanced pack and how ensure it starts to happen when charging. Thanks. 

[US69]

2 minutes ago, WARPed1701D said:

 Some great info here about the importance of balancing the pack regularly, side effects of an imbalanced pack and how ensure it starts to happen when charging. Thanks. 

If you are really interested in charge values and all the things going on, i highly recommend a Charge Doctor V2!

with that tool you can monitor your batterie status, voltage, the Watthours and amps that have been loaded, and so on and so on....

with it you can also adjust to stop charging at a specific voltage or percentage....for example 90% or 66 Volt.

in the states ewheels.com is selling this great little tool!