battery maintenance — storing an EUC for 3 months

[Chriull]

2 hours ago, RagingGrandpa said:

For the cells, 0% is 2.5V and 100% is 4.15V. 
Linear approximation gives:
40%: 3.16V/cell, 75.8V for 24s
50%: 3.33V/cell, 79.9V for 24s

As between 2.5V and 3V is not really much charge and the 2.5V are more a minimal threshold than a recommended operationial range this linear approximation does imho not fit. This 3.16V to 3.33V are afair the ?30%? maximum allowed voltage for transportation.

For storage afaik some 3.5V-3.7V as "internal ?equilibrium?" voltage of li ion cells is recommended.

But i got this only from some not to thoroughly readings afair. Would need to investigate batteryuniversity.com and some more googling again for some more knowledge.

[alcatraz]

Nominal voltage (50%?) 3.7v.

On some of these phone batteries where they burn the candle on both ends (4.40v) I've seen 3.75v I think.

[0000]

3 hours ago, Chriull said:

Would need to investigate batteryuniversity.com and some more googling again for some more knowledge.

Endless-sphere has a lot of good related battery data buried in various threads - example, this post by docware compares initial vs 700th cycle state of charge differences. Most of the cells tested are the 18650 format, but he did test the Samsung 50E cells which is probably reasonable to assume accuracy (with respect to his footnote disclaimer) for any other 5000 mAh capacity 21700 cell. Most interesting is the voltage at the 10% SoC threshold IMO.

His chart:

Edited October 7, 2023 by Vanturion

[alcatraz]

Hmm, isn't that particular study pointless?

I'm interested in the difference in impedance, heat generation, capacity.

[alcatraz]

Edit: I see that there'a capacity measurements as well in the link provides. Great. That leaves impedance and heat for a (to me) comprehensive test. 

[0000]

38 minutes ago, alcatraz said:

Hmm, isn't that particular study pointless?

You serious? This entire thread has been about what constitutes storage voltage for li-ion batteries. There was also some inaccuracies above about what voltages represented 40% and 30% state of charge/capacity. I'd be hard pressed to link a more relevant dataset to help clear things up. Maybe you can do better.

36 minutes ago, alcatraz said:

Great. That leaves impedance and heat for a (to me) comprehensive test. 

Great, I prefer steak over pizza except on Wednesdays.

[alcatraz]

Didn't mean to piss you off. 

Do you expect the optimal storage voltage to change after a couple hundred cycles?

Storing at 3.75v or 3.70v. Is that it?

[on one]

What would be the real danger of just leaving it plugged in the whole time? My Z10 stops charging and the charger is cold after the EUC gets a full charge. My Segway charger gets really hot to the touch while under full charging load. Or, could we give our batteries an 80% charge and then disconnect the battery leads?

My Kingsong 14D held a charge for like a year and went from 100% down to like 70%. If I had a V8, I think I'd just give it a full charge and then disconnect the battery leads. I'd probably do the same thing to my Z10 if I had to leave it unused for 3 months.

Or, let your friend use your wheel and learn to ride. It's probably best to keep your EUC in service if possible. You could sell it and then upgrade to a wheel with suspension when you get back. V8's have a good resell value.

Edited October 7, 2023 by earthtwin
one more thing

[Chriull]

28 minutes ago, earthtwin said:

. I'd probably do the same thing to my Z10 if I had to leave it unused for 3 months.

Be carefull - if you did not mod your Z10 there is some substantial drain even if turned off.

[on one]

I do have the @MRN76 but I didn't realize that the mod would prevent vampire drain. If I disconnect the batteries would the vampire drain still be a problem?

[Chriull]

2 hours ago, earthtwin said:

I do have the @MRN76 but I didn't realize that the mod would prevent vampire drain. If I disconnect the batteries would the vampire drain still be a problem?

No, the firmware mod afaik does not help. Here was some hardware mod shown to disconnect rhe communication between bms and mainboard when turned off. Afair.

But disconnecting the batteries should work well, too.

[goatman]

40 T's are more likely to self discharge at full charge than at 3.3v, ive put old salvaged packs in storage for over a year at 3.3v with no self discharge. 40T and 30 Q are known to self discharge above 3.7v to fully charged voltages 

[Dennis22g]

Does anyone know a good way to discharge the battery to a storage level from A fully charged state, without riding the EUC?   

[meepmeepmayer]

Just keep the wheel on and switch on the lights until your battery is sufficiently low for your liking.

[RagingGrandpa]

On 8/11/2024 at 8:33 AM, meepmeepmayer said:

Just keep the wheel on and switch on the lights

Upright the EUC so that it begins self-balancing, and lean it gently on a wall so that you can leave it there while it's on. 
Most models will time-out and automatically turn off within an hour like this, so many repeat wake-ups are necessary... 

[rcgldr]

Some manufacturers recommend charging to 80% or more for long term storage, which I assume would be due to particular EUCs having some small current draw even when turned off. Charging to 3.8 to 3.85 volts per cell would provide some margin for cells that self-discharge.

[RagingGrandpa]

  3.5V per cell, please.

On 11/2/2022 at 6:32 PM, RagingGrandpa said:

more evidence for the prevailing wisdom: store at low voltage (less than 3.5V/cell) and cool temperature (~10°C).

...because it minimizes capacity loss:

...and minimizes resistance change:

(Their definition of SoC was this.)

Low is good. Perfect to be between 3.0 and 3.5V.

[SoleCycle]

On 10/3/2023 at 11:40 PM, SoleCycle said:

I'm storing a wheel for probably 9 months. I'm looking for recommended...

Here's my 9 month storage report.

I brought the charge down to 50% based on what my EUC apps reported. Measured with a multi-meter, that showed an average of 3.717 v/cell. I unplugged the pack from the board to eliminate any chance of phantom loads. Measured the packs again after 9 months with the same multi-meter.

Before:  3.717 v/cell average
After:     3.692 v/cell average
Loss:     -0.025 v/cell over 9 months

I'm feeling more confident from how little discharge there was. I'll definitely bring the cell voltage down to 3.25 volts next time.

[alcatraz]

4 hours ago, SoleCycle said:

Here's my 9 month storage report.

I brought the charge down to 50% based on what my EUC apps reported. Measured with a multi-meter, that showed an average of 3.717 v/cell. I unplugged the pack from the board to eliminate any chance of phantom loads. Measured the packs again after 9 months with the same multi-meter.

Before:  3.717 v/cell average
After:     3.692 v/cell average
Loss:     -0.025 v/cell over 9 months

I'm feeling more confident from how little discharge there was. I'll definitely bring the cell voltage down to 3.25 volts next time.

Be careful. The charge isn't evenly distributed between 4.2v and 2.8v. The bulk of it is between 3.9 and 3.5v meaning you'll have the slowest discharge in that range but outside of that it will be much faster.

[SoleCycle]

On 8/14/2024 at 5:43 PM, alcatraz said:

The charge isn't evenly distributed between 4.2v and 2.8v. The bulk of it is between 3.9 and 3.5v meaning you'll have the slowest discharge in that range but outside of that it will be much faster.

I'm always down for refining my understanding but you're the first I've heard of this uneven storage discharge distribution. It wouldn't surprise me, but do you have any source for that info. On first look, it doesn't seem particularly compatible with the sources that RagingGrandpa have provided. What do you mean by much faster outside of the 3.5-3.9V range? How much faster? I mean, even if storing at 3.25V meant it self discharges at twice or triple the rate I experienced, that would still be less than 0.01 volts/month. Which seems worth it and reasonable if the lower storage voltage reduces cell degradation.

[RagingGrandpa]

Stored energy isn't evenly distributed between 4.2v and 2.8v

It's like this: 

So if you have some tiny bleed current happening during storage, over the next few years the cell voltage would follow the red line: decaying at a relatively constant rate until cell voltage is below 3.3V, then decaying more quickly.

As long as the cell voltage stays above 2.0V, there is no problem.
For very long term storage, powerup the EUC and check pack voltage every 6 months, to ensure it remains above ~3.0V average per cell. If lower than 3V, recharge a little.
For modern EUCs in good condition, there's no need to check it sooner than 6 months. 

If you're not sure, check voltage more often, like once a month- it's fast and ez. Make a note of each month's voltage to determine average decay rate, then plan accordingly.