Actual battery capacities vs claimed

[deflated tractioninterface]

OK, for this example I'll use the Monster V3 100V cuz that's what I have. Read to the end if you want to know the actual capacity of a monster battery.

Claimed capacity is an oddly specific 1845 Wh (1.845 kWh).

The cell in the Monster v3 100V battery is the Panasonic / Sanyo NCR18650GA per the Kebye specs.

You can read this cell's datasheet yourself by pasting the cell name plus the word 'datasheet' into google.

The capacity on the label is 3500 mAh, but the tested capacity is typically 3450 mAh. Guaranteed minimum capacity is slightly less.

The nominal voltage is clearly stated to by 3.6v, like basically every other non cobalt li-ion cell out there. 

The energy content of a cell in watt-hours or Wh is the product of the nominal voltage and Ah capacity.

Each individual canned cell has the following energy content given these charge capacities:

3.5Ah (too high)

3.6 * 3.5 = 12.6 Wh

3.45Ah (tested avg)

3.6 * 3.45 = 12.42 Wh

3.35Ah (guaranteed min)

3.6 * 3.35 = 12.06 Wh

A v3 100V Monster battery pack has 144 cells total. Presumably in a 24S / 6P config. The total energy content of the pack is the product of the per-cell energy content and total number of cells. 

So the ACTUAL full capacity of a monster's battery pack would be the following, other things equal...:

3.5: 1814 Wh

3.45: 1788 Wh

3.35: 1737 Wh

But, other things are not equal. The BMS probably doesn't full charge to 4.2, and 100/24 is 4.16. This lost energy content at the top is minimal, barely worth considering. But looking at the discharge graph, the BMS should cut off discharge in the 3Ah region. So with a completely new battery pack giving rated capacity, ridden in the best conditions with the lowest discharge rate, the actual energy content (ignoring slight additional loss at very top) available to the rider is:

3* 3.6 * 144 = 1555 Wh

Notice I said "ridden in the best conditions?" It's true, if you demand more discharge current from the battery pack, your average voltage will be lower while you will have the same amount of Ah charge available. So you will get less energy content out of the battery. We'll pretend things are optimal for our examples here.

And, now notice how I said "new battery?" The following varies by battery, but in general, for the few charge cycles, maybe a couple hundred, your charge capacity will diminish toward a stable plateau at maybe 80% of rated. This plateau will be stable for anywhere from a few hundreds to a thousand or more additional charge cycles depending on chemistry, environment and charge / discharge profile.

So the reliable capacity of a Monster v3 100V, in the best case, after battery capacity stabilizes, is:

.8 * 1555 = 1244 Wh

So, your capacity will start around 1.55 kWh, plateauing after some use around 1.24 kWh if you ride easy. That is still a big battery, and I think other riders might find these calculations interesting.

[alcatraz]

Yeah and cars have higher fuel consumption than advertised.

When the cells are used in vehicle applications and in arrays in series, there's no way to use the entire capacity that the cell manufacturer provides.

It's called nominal capacity for a reason. Functional capacity will be a lot less for all the reasons you stated. It's best if we continue to use one standard of measuring, be it nominal single cell capacity, than to mix several kinds. 

Something I'd like to see is a 100cycle degradation comparison between leading cells like 35E/18650GA/MJ1/etc. So many people care about 50Wh here and there and they don't even know if the brand of cell is the fast degrading kind or not. It doesn't matter if you pick a wheel with 2000Wh pack instead of a 1600Wh if after one year you're left with 1700Wh vs 1550Wh. It's wasted money.

Edited June 5, 2020 by alcatraz

[Ben Kim]

The issue is Gotway uses 3.7v as the nominal voltage as opposed to 3.6 (manufacturer spec).  88.8V nominal * 3.45Ah = 306.36Wh * 6p = 1838.16Wh.

[meepmeepmayer]

"100V" means 100.8V, they just don't write it out.

They use 3.7V nominal.

One 24s2p pack is rounded up to "615Wh" (~613Wh with 3.7V, ~596Wh with 3.6V), and three times that is 1845Wh, so that's where that number comes from (e.g. 1230Wh 100V wheels have two packs).

No defending anything, just explaining. Doesn't matter anyways as long as battery capacities are comparable*, which is the point.

(Besides some wheels having different 0% voltages, it works quite well.)

[deflated tractioninterface]

The point of this thread is to provide empirical info on battery capacity that some people may not have been aware of--not to offer opinions. The only opinion I will offer is that I am very happy with my Monster and its large battery.

The 3.6 vs 3.7 thing is really less significant than the lower cutoff capacity you don't get from the BMS. And obviously, the nominal voltage is not 3.7...that's imaginary. 

Maybe someone will find my calculations and explanation in the OP interesting. 

[dmethvin]

Not sure why people get hung up on a few tens of watt-hours in the battery spec. The EUC makers are just repeating the best-case conditions the cell makers use so there's no deception past the over-optimistic claims of any other manufacturer. There are so many variables here that it hardly matters. Actual range depends more on rider weight and ambient battery temperature than the fuzzy specs the cell manufacturers use, which of course are based on perfect conditions. If you charge to 100% every day in order to hit those lofty voltage numbers it hurts the battery lifetime. 

If you want to get better range and have the battery last longer I have three pieces of advice. 1) Lose weight 2) Go slower 3) Don't charge to 100% every time.

[deflated tractioninterface]

9 minutes ago, dmethvin said:

Not sure why people get hung up on a few tens of watt-hours in the battery spec. The EUC makers are just repeating the best-case conditions the cell makers use so there's no deception past the over-optimistic claims of any other manufacturer.

For real? The post specifically demonstrates that this is not the case while giving you the tools to validate my work. Dude you're a mod, the least you could do is read my post before replying.

[mrelwood]

2 hours ago, deflated tractioninterface said:

than the lower cutoff capacity

The BMSs on EUCs have not had a low voltage cutoff since circa 2015.

30 minutes ago, dmethvin said:

If you charge to 100% every day in order to hit those lofty voltage numbers it hurts the battery lifetime. 

And if you don’t, the imbalance will kill a cell group or a few even sooner...

[deflated tractioninterface]

5 minutes ago, mrelwood said:

The BMSs on EUCs have not had a low voltage cutoff since circa 2015.

So EUCs have no battery cutoff? There is a capacity cutoff of some kind, or you can ruin the pack irreparably on the first discharge. At some point the unicycle will tilt back / refuse to go. Aside from actual damage if you discharge a pack beyond a certain point the cell groups will go out of balance and take long and longer to rebalance. I mean, really guys? 

Edited June 6, 2020 by deflated tractioninterface

[mrelwood]

4 minutes ago, deflated tractioninterface said:

So EUCs have no battery cutoff?

At least not in a sense that would affect the usage. I don’t know if there is some kind of programmed behavior at avg 2.5V/cell or such, but it is way below what the wheel can be used down to.

4 minutes ago, deflated tractioninterface said:

At some point the unicycle will tilt back / refuse to go.

Exactly, it’s a programmed firmware feature. Not a cutoff.

 If you don’t know or remember, the early EUCs did have an actual low voltage cutoff, but after a few crashes the tips on how to bypass the feature by soldering a jumper wire onto the BMS got spread and the manufacturers were pressured to remove the feature. And they did.

 It is the largest difference between an EUC BMS and an e-bike BMS for example.

[deflated tractioninterface]

OK I will put a shunt in this thing and report back. Nothing beats empirical data. 

[Ben Kim]

1 hour ago, dmethvin said:

Not sure why people get hung up on a few tens of watt-hours in the battery spec. The EUC makers are just repeating the best-case conditions the cell makers use so there's no deception past the over-optimistic claims of any other manufacturer. There are so many variables here that it hardly matters. Actual range depends more on rider weight and ambient battery temperature than the fuzzy specs the cell manufacturers use, which of course are based on perfect conditions. If you charge to 100% every day in order to hit those lofty voltage numbers it hurts the battery lifetime. 

If you want to get better range and have the battery last longer I have three pieces of advice. 1) Lose weight 2) Go slower 3) Don't charge to 100% every time.

Actually with the tiltback engaging at 3.1-3.3V per series you are effectively using 75% of your battery’s capacity; thus cycle life is by default greater than the typical 300 stated by battery manufacturers. 

You also fail to understand that battery capacity is also diminished by age, and that alone will account for more loss than charging to 100% will ever do. 

I charged EVERY PEV i’ve owned to 100% like clockwork; the second i get home it goes on the charger. Each and every one of them charges and holds full voltage even after a year of ownership. 

Unless you have unrealistic fantasies of keeping your EUC for 10 years, don’t even bother with all this partial charging. Your battery will get hit by age before you reap any benefits from partial charging. 

(for reference, 300 full charge cycles on a 1600Wh battery pack, would net 12000 miles; I can’t think of many that have such numbers). 

[deflated tractioninterface]

3 minutes ago, Ben Kim said:

Your battery will get hit by age before you reap any benefits from partial charging.

Totally right. Unless your stock device is charging HV Lipo to 4.3 / cell every time you should let the device charge itself and and just ride. Most Li-ion last 5+ years. I see no reason why this isn't the case with my EUC. 

Edited June 6, 2020 by deflated tractioninterface

[mrelwood]

51 minutes ago, Ben Kim said:

don’t even bother with all this partial charging.

More importantly, battery packs getting unbalanced and eventually failing because of partial charging has become almost a weekly thing on this forum. It’s really sad.

1 hour ago, deflated tractioninterface said:

OK I will put a shunt in this thing and report back. Nothing beats empirical data. 

To be clear, “cutoff“ as a term is used to describe something being completely and suddenly turning off. A low battery tilt-back isn’t a cutoff, it’s a designed and programmed feature. Overlean also isn’t a cutoff, it’s overpowering the wheel’s balancing power capabilities. A wheel turning off mid ride (and causing a crash) is a cutoff.

[Ben Kim]

another tip to gain some range is to use the lightest tire you can find (i’d start my search with Kenda tires) and pump that tire to the maximum allowable psi. These things put out the equivalent of 2.6bhp (assuming 2000W nominal), unsprung weight (borrowing a car term) is an absolute killer when it comes to relatively underpowered electric vehicles. 

Edited June 6, 2020 by Ben Kim

[Ben Kim]

3 hours ago, deflated tractioninterface said:

Totally right. Unless your stock device is charging HV Lipo to 4.3 / cell every time you should let the device charge itself and and just ride. Most Li-ion last 5+ years. I see no reason why this isn't the case with my EUC. 

I still have a stash of 10 year old VTC4s that still hold some charge!

[mrelwood]

2 hours ago, Ben Kim said:

I still have a stash of 10 year old VTC4s that still hold some charge!

When talking about battery life time (300-500 cycles etc), usually a capacity loss of 20-30% is what is used as the reference point.

[Daley1]

I like martys, take on batteries. Charge em up and just ride. Its not rocket surgery! Keepin it simple!

[dmethvin]

Quote

You also fail to understand that battery capacity is also diminished by age, and that alone will account for more loss than charging to 100% will ever do.

Maybe? I've had several battery packs and EUCs that have sat idle for a year at partial charge without any appreciable issues. OTOH I have had many devices "sit on the charger" for two years and go bad. If Li-Ion battery packs generally last 5 years no matter what you do, then yes the EUC wrapped around it is likely to be obsolete before the battery pack goes bad. That hasn't been my experience though. The battery has gone bad first.

Quote

I charged EVERY PEV i’ve owned to 100% like clockwork; the second i get home it goes on the charger. Each and every one of them charges and holds full voltage even after a year of ownership. 

But 300 topped-up charges are about the point where the battery starts to degrade, so that experience doesn't contradict anything. The question is if you can get to 600 charges after about two years without degradation. If 5 years is the life of the battery due to age and 300 charges to 100% is when it starts to degrade, then partial charges would be beneficial?

Quote

More importantly, battery packs getting unbalanced and eventually failing because of partial charging has become almost a weekly thing on this forum. It’s really sad.

Balancing charges *are* really important. They're just not needed on every charge.

Quote

(for reference, 300 full charge cycles on a 1600Wh battery pack, would net 12000 miles; I can’t think of many that have such numbers).

As I understand Li-Ion batteries, a charge to 100% is a "full charge cycle". The reason to charge to 80% or so is that it doesn't count as a full cycle and stresses the battery less. Most people don't go from full-charge to low-charge on every trip. If you tend to go for example from 100% to 65% in a day then recharge to 100% you're "wasting" a bunch of charge cycles and getting a lot fewer miles but still aging your battery. So instead of 12000 miles you might only get 4000. 

 

 

[Chriull]

26 minutes ago, dmethvin said:

As I understand Li-Ion batteries, a charge to 100% is a "full charge cycle".

No. From 0-100% is one full charge cycle. Every fraction of it is the according fraction of a charge cycle.

Not "using the outer extremes should stress the battery less - but as you stated above not charging to 100% does not balance the cells. Imbalanced cells can degrade the pack more than the stress induced by charging to 100%.

29 minutes ago, dmethvin said:

Balancing charges *are* really important. They're just not needed on every charge.

Imho depends on the "balancing state" of the cells. As long as they are balanced (which normaly noone knows) no balancing is needed. They more they get outbof balance, the more balancing is needed. Balancing is not "perfect" and it cannot balance cells to much out of balance.

So if, how, when and how often balancing is needed is hard (to impossible) to say...

[Ben Kim]

3 hours ago, dmethvin said:

Maybe? I've had several battery packs and EUCs that have sat idle for a year at partial charge without any appreciable issues. OTOH I have had many devices "sit on the charger" for two years and go bad. If Li-Ion battery packs generally last 5 years no matter what you do, then yes the EUC wrapped around it is likely to be obsolete before the battery pack goes bad. That hasn't been my experience though. The battery has gone bad first.

But 300 topped-up charges are about the point where the battery starts to degrade, so that experience doesn't contradict anything. The question is if you can get to 600 charges after about two years without degradation. If 5 years is the life of the battery due to age and 300 charges to 100% is when it starts to degrade, then partial charges would be beneficial?

Balancing charges *are* really important. They're just not needed on every charge.

As I understand Li-Ion batteries, a charge to 100% is a "full charge cycle". The reason to charge to 80% or so is that it doesn't count as a full cycle and stresses the battery less. Most people don't go from full-charge to low-charge on every trip. If you tend to go for example from 100% to 65% in a day then recharge to 100% you're "wasting" a bunch of charge cycles and getting a lot fewer miles but still aging your battery. So instead of 12000 miles you might only get 4000. 

 

 

You would not want a wheel at the full 4.2V per series if it is staying in storage.  The assumption is that most will ride their EUCs at least once a week, not once a year.  In a storage state, you'd want to keep the cells cool/cold and close to nominal voltage to retain the most capacity upon reuse.  Perhaps I should have been more clear.

You'd get 600 partial charges, short changing yourself for no good reason because, like I said, age will get the cells before the cycles do.  I like getting full performance and full range out of the batteries I paid for. 

And no, any charge to 100% is not a full charge cycle.  If you drained your 100% battery to 50%, then charged it back to 100%, that is a half cycle.  With that said, using Gotway wheels as an example, given that their wheels quit working at 3.3V, each charge from 3.3V to 4.2V is roughly 0.75 of a charge cycle.  This all goes back to my original point though, age will hit the battery's capacity before charge cycles do.  

 

[deflated tractioninterface]

18 hours ago, mrelwood said:

More importantly, battery packs getting unbalanced and eventually failing because of partial charging has become almost a weekly thing on this forum. It’s really sad.

To be clear, “cutoff“ as a term is used to describe something being completely and suddenly turning off. A low battery tilt-back isn’t a cutoff, it’s a designed and programmed feature. Overlean also isn’t a cutoff, it’s overpowering the wheel’s balancing power capabilities. A wheel turning off mid ride (and causing a crash) is a cutoff.

OK, what I mean by cutoff is beyond a certain point of charge capacity the device will not allow you to discharge the battery further. The lead up to this can be whatever you want.

3 hours ago, Chriull said:

No. From 0-100% is one full charge cycle. Every fraction of it is the according fraction of a charge cycle.

Not "using the outer extremes should stress the battery less - but as you stated above not charging to 100% does not balance the cells. Imbalanced cells can degrade the pack more than the stress induced by charging to 100%.

A charge cycle is a discharge followed by a charge to whatever respective bottom and top limits you define. Basically no manufacturer's programming allows full discharges, or close with lithium ion in practice and many don't do full charges. 

Battery management can be programmed however you want. Many BMS will stop charge and full balance at any point you want. But, as pointed out several times above, this is mostly irrelevant, and it wouldn't bother me if my Gotway full charges to 4.2 every time. The battery will still probably outlast my use of the device. On the other hand, even one single too low discharge can permanently ruin the battery and render it unsafe, so the low end is much more conservatively protected. I have no complaints.

[mrelwood]

5 hours ago, deflated tractioninterface said:

OK, what I mean by cutoff is beyond a certain point of charge capacity the device will not allow you to discharge the battery further.

That explains. That's not what a cutoff means though, as it doesn't cut anything and it doesn't for example turn the wheel off. What you describe is the low battery tilt-back of the firmware. Low voltage cutoff is a BMS "safety" feature. BMSs for non-self-balancing vehicles do usually have an actual low voltage cutoff.