Battery Longevity

[hyiu00]

Recently I have been reading articles on the internet about lithium ion battery.  What I want to know is if I do not use my unicycle for a long while, how should I keep it to increase the longevity of the battery.  I found two main points: keep it at around 15 - 20 degree C, and the battery charged to about 40 - 50%.  But to be able to do this, I most likely have to disconnect the battery cable directly as most unicycle still draws some small current even when powered off. 

Now I am wondering does anyone be able to keep their unicycle for a few years and still be in good working condition?  If not, does it just reduce the travel distance (due to lower capacity) or it actually increase the chance of face planting (due to increase output resistance)?

[Fahrtwind]

I fly electric model helicopters and usually in wintertime prefer flying gas powered ones. To keep the batteries in best conditions, store them as cool as possible but above 0°C (don´t freeze them). This slows down chemical reactions. I put them in the fridge in winter time. Of yourse, you have to disconnect/get them out of the EUC. And as you stated correctly, there should be a level of 40-50%. Usually I don´t have to recharge them for months, the level does not drop.

Important: to charge/discharge Batteries, they should be warmed up to room temperature again!

[charlie - uk]

"The best place for your Lithium batteries is in the fridge"

No, No No, this is the worst advice I have ever heard. As a profesional working with lots of Lithium & NIMH batteries, the best place for your batteries is in a moderate temperature room that gets, not too hot or cold. Avoid extremes of any temperature. In a domestic situation, usually, the most acceptable storage environment is in the living or family room as this is the room which is usually kept to reasonable temperatures. If you have to leave the battery unused for a lengthy period, make sure it's about 3/4 charged. Disconecting the battery from the EUC, might be a good idea to prevent long term parasitic drain of current.

Storage of batteries in a domestic situation, is a bit of a problem, because ideally you want to keep your batteries, in a metal cabinet, to protect against danger of fire, but most people don't have the luxury of setting aside a heated, smoke alarmed battery storage area so, living room, or family room it is...

[Fahrtwind]

I was talking about storage only, you should not charge or discharge a battery at low temperature. The Lithium battery ages because of chemical degrading caused by chemical reactions. It is a fact, because of thermodynamics, chemical reactions can be slowed down by lowering the temperature and slow down"aging". Works with food and: batteries. But again, using the battery when cold is bad because of the high inner resistance. 

But the best way: just drive your wheel all over the year...

[Pingouin]

Hi,

I have been keeping lithium polymer, lithium ion and lithium phosphate batteries for more than 10 years, I found that for the best longevity, you must:

- store them in a cold dry room, I mean between 1°C and 10°C is the best (however, if you keep them in a 22°C room, it's fine it's just going to loose a little more capacity over the years)

- store them at 60% is perfect (you can do that either by recharging them to that level, or discharging them (avoid keeping them at 100% as it ruins the batteries)

- always have the cells balanced before using them because if one of them get's too low on voltage it can harm it

- never charge above 0.5C, if it's a 8.8Ah battery, do not charge it over 4.4A, fast chargers are not good for the batteries

- avoid extreme temperature (above 30°C don't output too much watts, and below 0°C same thing)

- try charging and discharging them at least once every three months

- avoid discharging the batteries below 10% too often for li ions, 20% for li pos

- wait 10-20 minutes after full charge before riding

- wait 2h after riding to recharge them

I would add that yes the batteries are always connected to the EUC, it might drain a little more power even if you don't use it, so check every month your remaining battery if you don't use it, just for security.

Anyways, I think if you don't go too hard on the batteries, even if you don't follow my advices, the batteries will last longer than your EUC if you are riding often (2000km per year), I have batteries that are 7 years old, and lost about 35% of their capacity but they still work ok. I'd say that in general for a normal usage, over 5 years, batteries should be replaced.

[Keith]

I've run out of credits for today, sorry guys but @Fahrtwind and @Pingouin are correct. At a storage charge of 3.8-3.85V per cell (or anywhere near 50% indicated charge) cold conditions are best and reduce degradation significantly. However do not take our word for it (and certainly not @charlie - uk) it is all covered in detail here:http://batteryuniversity.com/learn/article/how_to_store_batteries. The details on that site reflect what the 3 of us have individually found operating model radio control Lithiums which are treated much harsher then our EUC batteries.

The confusion may be because, cold temperatures increase internal resistance and damage under load and if stored very cold whilst fully charged it produces an overcharge condition in the battery which will quickly damage it. I.e . Store low temp, but charge and use as near room temp as possible. I invariably used to lose batteries flying in the winter, never in summer until I kept them in a heated bag at the flying field.

There is no need to cycle a stored battery but check its voltage once a month or so and top up if it is dropping below 3.8V per cell (40% on the wheels indicator) 

If there is a current drain from the device then charging back to 60-70% each time won't do any harm.

[Pingouin]

I would add, if you use your EUC often, don't hesitate to recharge before it reaches 10-20%, it's better for the cells than waiting until deep discharge. Time and bad storage is the worst enemy of battery longevity, more than a frequent use (except overloading your EUC, or always discharging your battery with high peaks (more than 3C, for a 8.8Ah it would be 26A).

[mhpr262]

I wonder why manufacturers still use those cylindrical laptop cells - it must be due to the price. Modern LiPo pouch cells meant for R/C models, like the latest Turnigy Graphene from Hobbyking can be discharged at continuous rate of 65C and a pulse discharge for a few second of twice that, 130C - meaning you can pull 650 Ampere out of a 5.000mAh pack. The copper windings in the motor would turn into slag before the battery cut out on you with that kind of power (as long as the battery is still charged of course).

http://www.elektromodellflug.de/turnigy-graphene.php

[esaj]

2 hours ago, mhpr262 said:

I wonder why manufacturers still use those cylindrical laptop cells - it must be due to the price.

Safety, availability and price would be my guess, not necessarily in that order. A metal-cased 18650 can take a hell of a lot more beating before getting pierced (and "venting with flame") than a LiPo-pouch.

[mhpr262]

Safety is big issue, I'm sure, especially after the disaster with the Hoverboard fires and ban. We definitely don't need that with the unicycles. That said, they are much safer than they used to be even a few years ago. I use "soft" pouch cells in my offroad R/C cars and they really get abused in that function, both in regards to physical hits and electrical loads, but I have never had even the slightest issue. The official R/C racing series still prescribe the use of plastic-enclosed hardcase lipos, though.

[Keith]

On 11 August 2016 at 0:58 PM, esaj said:

Safety, availability and price would be my guess, not necessarily in that order. A metal-cased 18650 can take a hell of a lot more beating before getting pierced (and "venting with flame") than a LiPo-pouch.

It is pretty much the same technology with the similar  energy density but with discharge rates we don't need. Who needs an EUC with fragile, easily damaged batteries that flattens them in 3 minutes (20C discharge.) - well other than @EUC Extreme of course :-). 

They are getting better but I am not at all convinced LiPos last well. I used to be lucky to get 2 years out of a LiPo before at least one cell puffed up, I'm now getting, perhaps 4 years, what I cannot be sure about is whether that is down to improvements in the cells or just my being a lot more careful about use and storage - something the average consumer would not do.

[OliverH]

On 11. August 2016 at 11:10 AM, mhpr262 said:

I wonder why manufacturers still use those cylindrical laptop cells - it must be due to the price. Modern LiPo pouch cells meant for R/C models, like the latest Turnigy Graphene from Hobbyking can be discharged at continuous rate of 65C and a pulse discharge for a few second of twice that, 130C - meaning you can pull 650 Ampere out of a 5.000mAh pack. The copper windings in the motor would turn into slag before the battery cut out on you with that kind of power (as long as the battery is still charged of course).

http://www.elektromodellflug.de/turnigy-graphene.php

Graphene batteries are supposed to have 1/4 volume of the 18650 batteries at the same energy. That would be good to our EUCs.

[Keith]

2 hours ago, OliverH said:

Graphene batteries are supposed to have 1/4 volume of the 18650 batteries at the same energy. That would be good to our EUCs.

Really! There are lies, damn lies and statistics. Compared with a cheap standard LiPo they are no giant leap forward:

The below figures directly from Hobbyking's website:

Turnigy Graphene 2200mAh 3S price £23.14 (equivalent price for 16s 840Wh =£795)

Specs:
Capacity: 2200mAh
Voltage: 3S1P / 3 Cell / 11.1V
Discharge: 65C Constant / 130C Burst
Weight: 225g (including wire, plug & case)
Dimensions: 106x35x31mm
Balance Plug: JST-XH
Discharge Plug: XT-60 

Zippy Flightmax 2200mAh 3S price £9.09 (equivalent price for 16S 840Wh=£313)

Spec.
Capacity: 2200mAh
Voltage: 3S1P / 3 Cell / 11.1v
Discharge: 25C Constant / 35C Burst
Weight: 173g (including wire, plug & shrink wrap)
Dimensions: 104x36x25mm
Balance Plug: JST-XH
Discharge plug: XT60

Heavier, bigger, more than double the price - exactly what you would expect from a high discharge LiPo compared with an average discharge one!

Oh and the 1 review says;have been using these for 2 weeks in my T-28. They have the same power and time in the air as my other lipoly batteries. I am using the 65c version but they seem to perform the same as my other 65c batteries. Maybe they will last longer in the number of times you can charge them."

[Pingouin]

Hi, the turnigy graphen are meant for extrem uses in RC modelling, like 3D flying, with extreme high pics of demanded current. A battery capable of sustaining 65C (143A with the 2.2Ah) and 130C in burst (286A), in our example, this means that in burst of 3s, this tiny 3 cell lipo can deliver 3603W  and 1801W all the time !

What I mean is that the zippy flightmax this small can't be used for an EUC, because of the small discharge current values (441W in burst..), i would need at least 4 times the capacity to be able to resist in an EUC.

Compare that to a standard 3S2P 4400 mah 18650 li ion battery pack weights 300g. It has a max discharge current of 1C, which means... 4.4A ! (at 12V, not at 67.2V). I think that the turnigy graphen, for EUC, is not needed, the extra rated "C" discharge will only bring added weight, a 10C lipo would be much more appropriate I think. I have never seen a li ion, at the same discharge rate, being able to be lighter than a lipo. I had a 3S1P 18 350 mah that weight 770g for a 3C discharge rate, if I was to put several of them to have the equivalent of a li ion 18650 type, they would be much lighter and with a higher discharge rate.

[US69]

LiPo cells do not deliver the same amount of watthours on the same place as our LiIon cells ...and graphene LiPo needs even more place!

take a look at following thread where someone puts 4 "normal" lipo cells of 4 x 10000mah cells into his MCM...MCM is absolutly full packed! 

with this configuration he has 592 Watthours....if he had used the Graphene...on the same place!!! he could only do 4 x 8000mah...so just 4/5 watthours = 473! And also the graphene where much more expensive...so he chose normal turnigy...

so now what can you get max with LiIon? you take 2 x 414 watthour batterie packs = 828 watthours!

Sure the LiPo cells are good for draws of high current...i also have some mind games of packing my 1360wh Ks18 full with LiPo's and i allready checked the max Watthours i can achieve with the place that is there...

i come to an absolut max of about 1000watthours...with much luck to 1100...when using LiPo's!

with LiIon you can do a max of 4 x 414 = 1656watthour...not possible to press so much LiPos in the Ks18 to get to this numbers!

As 1100 with LiPo's can be enough for me...i will nevertheless try this with the LiPos when i ever run into batterie problems...because of the none existing voltdrop and the better behaviour under "pressure"....AND LiPo are cheaper :-)

[OliverH]

2 hours ago, Keith said:

Really! There are lies, damn lies and statistics. Compared with a cheap standard LiPo they are no giant leap forward:

The below figures directly from Hobbyking's website:

Turnigy Graphene 2200mAh 3S price £23.14 (equivalent price for 16s 840Wh =£795)

Specs:
Capacity: 2200mAh
Voltage: 3S1P / 3 Cell / 11.1V
Discharge: 65C Constant / 130C Burst
Weight: 225g (including wire, plug & case)
Dimensions: 106x35x31mm
Balance Plug: JST-XH
Discharge Plug: XT-60 

Zippy Flightmax 2200mAh 3S price £9.09 (equivalent price for 16S 840Wh=£313)

Spec.
Capacity: 2200mAh
Voltage: 3S1P / 3 Cell / 11.1v
Discharge: 25C Constant / 35C Burst
Weight: 173g (including wire, plug & shrink wrap)
Dimensions: 104x36x25mm
Balance Plug: JST-XH
Discharge plug: XT60

Heavier, bigger, more than double the price - exactly what you would expect from a high discharge LiPo compared with an average discharge one!

Oh and the 1 review says;have been using these for 2 weeks in my T-28. They have the same power and time in the air as my other lipoly batteries. I am using the 65c version but they seem to perform the same as my other 65c batteries. Maybe they will last longer in the number of times you can charge them."

There's a US based start up bought by Bosch and they claim for the values 1/4 of size.

[Keith]

42 minutes ago, OliverH said:

There's a US based start up bought by Bosch and they claim for the values 1/4 of size.

Graphene has the potential for higher energy density, much faster charge times, and environmental improvements. Ironically it is highly likely they will be made in 18650 form factor so we will may stil end up using "those cylindrical laptop batteries". In fact, if I understand correctly it doesn't replace the existing chemistry at all, it is just used as a more stable, more conductive layer within existing LiIon, LiPo and LiFePO4 cells.

However we were specifically  talking about Turnigy Graphene batteries which (IMHO) based on their specs and form factor are ordinary Lithium Polymers with a VERY naughty name! Least wise if they have added Graphene it hasn't achieved anything except higher discharge rates - I.e. Lower internal resistance.

@KingSong69's link however is very interesting, and I missed it when originally posted. Full credit to @Samppa for doing a really excellent job of converting to Lithium Polymer. I hope (hint hint!) that he keeps us informed how the perform over time.

[Samppa]

i dare say that 592 lipowatthours will be "better" than 680 li-ionwatthours. I had 340Wh original li-ion battery. With it I was able to drive only ~15 km. After that voltage was dropped too low in my mind. Now with 10Ah/ 592wh lipos i can quite easily drive 50km and batteryvoltage is still almost 59V (~3,68V/cell) after short cooldown. Lipos give almost full power out until they are totally empty. So voltagedrops are minimal even under full acceleration uphill. I normally don't discharge lipos under 40%. 3,6V/cell is last limit, otherwise the battery may suffer.

I do not have bms, but lipos seems to stay in perfect balance without it. Over ten charges behind after last balancing and there are only 0.01V differences between all cells. I have begin to doubt that I can run "forever" without need of balancing cells. They even seems selfbalancing themselves when euc is not in use. Low charge/discharge amps will probably make possible that balance stays so good. I charge at 0,175C and discharge amps normally are between 5-10A. Short peaks can go over 30A. But batterypack can deliver 100A constant and 200A peak (10s) so it's not problem. Discharge C is between 0,5-5 and in 90% of time its somewhere between 0,5-1C. I will continue to report on how the journey continues with lipos...

[Samppa]

Now it is more than twenty battery charges and over 600km behind without need of cell balancing. Just checked and differences were still max 0.01V between all cells. Looks still very good.