Battery life, in years.

[Waverider216]

I’m thinking of purchasing a wheel that has roughly 600 miles and about 40 discharge cycles.  The wheel was bought almost two years ago.  Is there a point where the age of the unit (and battery) affects the battery more than the mileage and discharge cycles?  Will consistent use keep the battery in “shape” regardless of time?  Thanks in advance 

[someguy152]

supposedly if you can keep the battery stored at 50% and in cool temperature, a researcher who does batteries for tesla said these 18650's should show minimal degradation....but most likely that did not happen with ur wheel and even if you were to try, you might not exactly be sure if ur cells are balanced as none of these devices have monitors on them that measure the cell voltage of EACH particular cell in series.

[Bob Eisenman]

I've read 2 years or 200 cycles too.

Edited April 27, 2020 by Bob Eisenman

[.....]

If its only 300 cycles, I guess thats roughly $0.11cpm in battery life alone(300 cyclesx30 miles = $800 packs), on my 18L. Damn scary number adds up fast. Gas in my car is only $.08cpm. It is really sad to know that no matter how much we try, these wheel batteries do have a relatively short life cycle. I guess it kind of depends on how bad youll let them get, before you consider them below acceptable. Tbh, I have some lion packs here that are well over 5 yrs old and perform like new, just not in my wheels. Ive some 9yr old gopro batteries that still work decent.

Edited April 27, 2020 by ShanesPlanet

[mrelwood]

E-car and e-bike batteries have a few crucial differences in the included cell management that make them unfit examples on the best EUC battery practices. What I've been able to learn and experience during the three years of riding is that there are two completely separate aspects that can make an EUC battery pack useless:

1. Individual cell groups dying, caused by bad balancing or other preliminary cell failure.
2. Degradation (loss of capacity and/or power).

The latter is supposed to happen at 200-600 (-1500) full cycles, which on modern big battery wheels translate to 20 000 km and upwards.

But the former is the one that killed one of my 16S's packs at 4000 km, the other at 8000 km, and we have seen it happen at as low as around 2000 km. So bad balancing is ten times as much of an issue as battery degradation. I haven't actually even heard of a situation where a failing battery pack (or a notable loss of capacity/power) would not have been explained by preliminary cell death.

Due to this I now balance charge at least on every other charge, usually on every charge. My MSX is at 11 000 km without noticeable battery degradation.

 

So much for the usefulness of 80% charging...

[Waverider216]

So would a good screen then be to ask the seller to fully charge the wheel and see if it gets to 84V?  Assuming the battery pack in the wheel is around 2 years old, that would be the bigger factor in possible cell death rather than the discharge cycles since it has only 600 miles.

[.....]

Ending voltage is probably the only easily verified check you can do before buying a used wheel. I would think its both a good idea and not too much to ask, to see that a wheel can get to full charge, prior to purchase. No other single parts is as expensive as battery packs.

I too top mine off and 'balance' charge my wheels almost every time after a ride (after I let them sit for an hour to cool). I'm not a fan of having to watch them charge and then hope i unplug them at 80% and THEN compromise my range (which is barely enough) or have to wait to top off a wheel before leaving. Once I collect a lot of wheels and it seems that some may sit inactive for months... If I charge them to 90%, wouldnt they drop back to 80% at rest? MAYBE I'd balance charge them for a LONG time, then ride them down to 70% for storage. Of course, i ride down to 70% and they will bounce back to 80% after resting. But, ONLY if i had wheels that intended on sitting for months. Then theres the caveat, if i only charge to 80% and long term storage, will they reach a dangerously low level sooner, than if i had just cahrged to 100%? How long does a 100% charge take, to drop to 80% from storage? Its too damn much for me to worry about.. Charge it, ride it, rinse and repeat.  I really hope that too many wheels for long term storage,  becomes a problem for me

Edited November 20, 2020 by ShanesPlanet

[mrelwood]

1 hour ago, Waverider216 said:

So would a good screen then be to ask the seller to fully charge the wheel and see if it gets to 84V?

That’s what I’d recommend, yes.

 

1 hour ago, ShanesPlanet said:

wouldnt they drop back to 80% at rest?

Li-ions have very low voltage loss after the initial small drop. A relatively healthy battery at 40% will still be at 40% 6 months later if not being used.

[Chriull]

4 hours ago, mrelwood said:

...

1. Individual cell groups dying, caused by bad balancing or other preliminary cell failure.
2. Degradation (loss of capacity and/or power).

... So bad balancing is ten times as much of an issue as battery degradation. I haven't actually even heard of a situation where a failing battery pack (or a notable loss of capacity/power) would not have been explained by preliminary cell death.

...

I'd say could be "ten times" of an issue - afaik depends very much on the original cell matching performed...

from https://batteryuniversity.com/index.php/learn/article/bu_803a_cell_mismatch_balancing :

So once a cell (group) "is out of sync" it goes down rapidly....

There is also some new parts in this batteryuniversity article:

"Applying a heavy load during acceleration, followed by rapid-charging with regenerative braking requires well-tuned cells in a high-voltage battery to attain the anticipated life"

"Adding cell balancing is beneficial especially as the pack ages and the performance of each cell decreases at its own pace. A problem arises when a cell in a string loses capacity or develops elevated self-discharge. This can be attributed to high-temperature spots in a large battery. Low-quality cells may also be prone to unequal aging."

So your 

4 hours ago, mrelwood said:

killed one of my 16S's packs at 4000 km, the other at 8000 km,

relatively early "single cell (group) death" seemes to arise from not good enough matched cells?

Or one needs to have "good fortune" that the charger voltage fits "good" to the balancing voltage thresholds of the BMS to get good enough balancing?

Or such passive balancing just is not enough for this kind of battery packs with this kind of burdens and the way the cells are matched (if at all)....

Or as @ShanesPlanet does, full saturation charge is needed (about) every time?

[mrelwood]

@Chriull I did see some measurements and conclusions stating that KS battery packs may have worse odds for premature death due to worse initial cell balancing and/or lower balancing current than competitors’ packs.

Of the “Not changing above 91%” threads on this forum it does seem that a few are related to a past Inmotion V10 bug, and the vast majority are KS wheels. A few old GWs as well, naturally due to their age and the misleadingly (or insufficiently) marketed 80% chargers that have had quite a good availability.

Edited April 27, 2020 by mrelwood

[Waverider216]

So the wheel I’m interested was charged to 99.08% and is reading 82V.  Charging over the years have been done with two regular king song chargers.  Could this have led to an imbalance instead of just using one charger?

[Chriull]

7 minutes ago, Waverider216 said:

So the wheel I’m interested was charged to 99.08% and is reading 82V.  Charging over the years have been done with two regular king song chargers.  Could this have led to an imbalance instead of just using one charger?

Which wheel?

Could be the wheel just reports wrongly 82V instead of 84V? That's ~2% deviation not nice but not impossible...

Whats the no load/maximum voltage of these chargers? Maybe both have a bit low voltage (misadjustment)?

KS wheels can be turned on while charging and the reported battery voltage logged while charging. One could see if the BMS cuts off prematurely by cell imbalances.

If the batteries are drained a little bit after such charging and (satiration) charging/slight drain is repeated a couple of times one could see if balancing improves...

 

[Waverider216]

It is a kingsong 18L.  The seller indicated that he stopped charging after one of the charger lights turned green while the other was still red.  So the 99.08% and 82v reading was after unplugging and rest. Would that remaining 1% still get the wheel back to 84V if charging for much longer?

[Chriull]

3 minutes ago, Waverider216 said:

It is a kingsong 18L.  The seller indicated that he stopped charging after one of the charger lights turned green while the other was still red.

Ah - both chargers were used in parallel and have different voltages.

3 minutes ago, Waverider216 said:

 So the 99.08% and 82v reading was after unplugging and rest.

So they cells were "never" balanced or charged fully.

3 minutes ago, Waverider216 said:

Would that remaining 1% still get the wheel back to 84V if charging for much longer?

I'd see no way to predict this - one should try to just charge with the higher voltage charger and look at the outcome.

Maybe some repetitions (with the slight draining inbetween) are needed.

[.....]

9 hours ago, Chriull said:

Ah - both chargers were used in parallel and have different voltages.

So they cells were "never" balanced or charged fully.

I'd see no way to predict this - one should try to just charge with the higher voltage charger and look at the outcome.

Maybe some repetitions (with the slight draining inbetween) are needed.

There's the possible answer. The chargers arent balanced exactly, and I'd bet one goes green way too soon, especially if another with higher voltage is pushing juice. I bet if he charges with the higher voltage output charger and leaves it for a few hours AFTER it tunrs green, youll see that it hits 100%. Maybe not, but when running both chargers, I could see how a person would never FULLY charge it, should they stop when ONE charger goes green. Waiting for BOTH chargers to go green, makes more sense to me. The charger that stops early, will more than likely just stay stopped, as the higher calibrated charger finishes. I dont leave on chargers overnight, but i left them on for hours after going green. Soon I'll have 3 chargers and 2 wheels, but rarely will i double up for faster charging, as slower charging is safer and in my opinion... easier on the cells.

Edited April 27, 2020 by ShanesPlanet

[Waverider216]

Just an update guys, I asked the seller to leave the charger on for a few hours with just one charger.  Voila it was 84v and 100%.  Thank you guys for the response and help.

[alcatraz]

On 4/27/2020 at 9:20 AM, Waverider216 said:

I’m thinking of purchasing a wheel that has roughly 600 miles and about 40 discharge cycles.  The wheel was bought almost two years ago.  Is there a point where the age of the unit (and battery) affects the battery more than the mileage and discharge cycles?  Will consistent use keep the battery in “shape” regardless of time?  Thanks in advance 

Some older Sanyo/Panasonic high capacity cells (NCR18650B, common chemistry with current cells) start at 100% and after a few hundred cycles dip below 80% capacity. After over 1000-2000 cycles the cells keep a capacity over 75% and the capacity drop has flattened off. They will basically stay there forever.

The problem is that the supplied BMS can no longer balance the cells adequately. It means that as the imabalances grow, the rather small balancing currents they provide are inadequate. It means you start to use the pack unbalanced and that's when it goes downhill real fast.

If you can manage to keep the pack balanced after thousands of cycles (requires monitoring, adequate balance currents) then the pack might outlive the rider.

Unforunately bms boards with good balancing currents aren't really used, generally. So everyone essentially slowly kills their own packs unknowingly, and blaming it on age/quality etc.

[null]

I’m ogling a second hand v8 as a gift, but as it is close to 4000km and three years old, I’d like to check if the battery is healthy. The price is decent (300€) so it might be worth it.

Even though it is probably down to 90% capacity, should it still be expected to charge to 84v?

Other than right voltage and keeping the charge is there any other thing that can be checked? 

As it’s a low price item I can’t go around testing it with charge doctors..

Thanks for any input.

[mrelwood]

On 11/17/2020 at 1:46 AM, null said:

Other than right voltage and keeping the charge is there any other thing that can be checked? 

If it charges up to 84V, I think you’re golden for a 300€ V8. Everything else is either too hard to measure, or not relevant enough. IMO.

[null]

6 minutes ago, mrelwood said:

If it charges up to 84V, I think you’re golden for a 300€ V8. Everything else is either too hard to measure, or not relevant enough. IMO.

👍🏻 Thanks, thought so, just needed to confirm wear shouldn't noticeably lower the voltage (failure do)

Edited November 18, 2020 by null

[Ben Kim]

certain wheels also do not charge full and it is normal operation. Both my mten3 and mcm5 record a full resting voltage of around 83.6V.