Dead Battery - EM Owners help!

Moderators, please move if I have posted in the wrong forum.

The bike is a 2016 EM Sport+ with a 16ah battery.

I may have ruined my battery. I forgot to turn it off and the battery is dead. When I plug the charger in the red & yellow bars flash but the relay does not trigger and the battery won't charge.

Is there a way to get the battery to take a charge?

Well, it's trying to protect you from a potential fire. Overdischarged cells can fail in various ways, some quite destructive, when recharged.

If you don't care about the risk, or just want to assess the severity of the problem, you can open it up and check the voltages on all the cell groups at the BMS wires, and see how bad the problem is first, listing all of those voltages here in the thread; we can give you an idea of whether they're really bad or just need a little boost.

If they're not much below 3.0v, even 2.8v, then they're potentially recoverable (but still with some risk, which is why the BMS won't allow the recharge).

If they're below 2v, especially way below that, I wouldn't do it; the risk itself is small but the consequences can be dire.

Thanks. I'll check the voltage before giving up.

here's where I'm at right now. We took it apart and found that there is a small charger relay that runs off on the first cell(s) in the pack. after charging those cells the battery charger started working. However it charged way too fast so we are still testing.

BTW, the Electric Motion (EM) help desk is fantastic. They are very prompt in responding to emails and even volunteered to talk by phone if needed.

What voltage were those cells at, for each cell?

If they were lower than 2v, I'd be concerned about their future reliability, or worse.

If they were lower than 1v, I'd be concerned about their future volatility; most common lithium cells that get severely overdischarged have a notably higher than normal chance of dramatic failure (fire, etc).

I don't have voltage before charging. After charging voltages on balance connector (starting from neg side)
4.041
4.021
4.035
4.033
4.056
4.025
4.048
4.030
4.028
4.051
4.033
4.035
4.002
3.992

I'm concerned about the near term life of the battery but if I can get through the trials season with it I'll be happy. My inter project is to rebuild this one (if necessary) and to build a second battery.

If there was no voltage before charging them, then they were at 0V.

That means they are potentially dangerously damaged, and could catch fire during charge or discharge, or even just sitting there, someday. (you can't know when; or even if, it will happen...but it has happened under these conditions).

So at the least I would make sure this is never kept in or near a building, as a precaution.


That's why the BMS doesnt' allow charge of an overdischarged battery.

Thanks will keep this in mind.

update - now reassembling the battery and going to take the bike out and practice for the next trials event.

Here's the latest details from Stephen

Aug 7 @ 5PM 55.77V
Aug 8 @ 5PM 55.70V

Aug.9 7AM
3.973
3.977
3.978
3.977
3.978
3.977
3.976
3.977
3.980
3.979
3.982
3.980
3.976
3.981

Started const 20A discharge test at 7:16am. (20A is ~1C rate on 18Ah battery.) 20A*~50V=~1kW.
Drops 1.4V loaded w/ delta 20A (20A -> 40A). 1.4V/20A=70mohm / 14S = 5mohm/cell. That seems high.
7:53am auto shutoff = 37m = 0.62h * 20A = 12.3Ah. Since battery was ~4V/cell when I started, I'd estimate *ROUGHLY* 75%SOC starting. 12.3Ah/75%=16.4Ah. Looks like you didn't loose much capacity. The cell resistance might just be higher now which will limit peak current. Nothing got hot at the 20A rate.

48.42V 8:03am (10min rest - battery slightly above room temp)
3.455
3.472
3.455
3.460
3.426
3.464
3.441
3.473
3.472
3.449
3.468
3.466
3.481
3.487

Recharged to 57.65 (4.12V/cell)

last update. It is holding its charge. put it back into the bike and did a shot ride. All seems well for not. Riding a trials vent Saturday and will know better then.

If your cells went low they are already damaged and will eventually short internally which can lead to a fire.

flat tire said:

If your cells went low they are already damaged and will eventually short internally which can lead to a fire.

Click to expand...

yup amberwolf has already pointed that out

If the BMS was doing it's job, it should have cut off at a safe voltage and prevent the cells from getting damaged. A slow drain is less damaging than full current at low pack voltages. Still, without knowing how low the cells got, there is an increased risk of pack fire so charge in a fire safe location.

From you voltages, the pack seems fine.

fechter said:

Still, without knowing how low the cells got

Click to expand...

He said previously that before charging, the cells had no voltage, which means they were drained to zero.

amberwolf said:

fechter said:

Still, without knowing how low the cells got

Click to expand...

He said previously that before charging, the cells had no voltage, which means they were drained to zero.

Click to expand...

I do not have the voltages at start. Keep in mind I'm new at this. The battery does disconnect when the voltage gets too low. I wish I had correctly tested it. It may have been zero or not.

Just to be safe I'm storing the battery in an area where there is no fire risk.

Rut Row said:

I do not have the voltages at start. Keep in mind I'm new at this. The battery does disconnect when the voltage gets too low. I wish I had correctly tested it. It may have been zero or not.

Click to expand...

Ok. Another post of yours said "I don't have voltage before charging." when I asked you specifically what the cell voltages were, which one interpretation of which implies that the cell voltages were zero, because a previous post said " I'll check the voltage before giving up." which implies somewhere between there you did check them, without a statement that says otherwise.

Another more loose interpretation could be that you did not measure the voltages before charging, but that is not what it sounds like. (but from what you say above, it is probably what you meant).

It's very important to be very clear with specific answers to specific questions when troubleshooting, because the results depend on that. We can only know what you tell us, and what we can deduce or imply from what you tell us. So what we tell you is based on that, and as the saying goes, "garbage in, garbage out"--if you tell us wrong information, you get wrong answers back.

If you have no idea what the cells were before charging, then they could all have been perfectly fine, and there may be nothing wrong with the pack at all, other than it was not charged sufficiently on the cells the "charging relay" runs off of. (whatever this "relay" actually is, and whichever cells those actually are). It may have a long and healthy life ahead of it....

Since you don't know, it *is* still safer to treat it as a fire risk, as you are presently doing.

If the BMS was tripped, the pack output voltage might read zero but the cells could still be in the healthy range.