Battery question: low voltage

[vext]

I have a brand new battery and charger that came with my e10/m600 and after the first 24hour charge the battery is only at 53.9v and not at the full 54.6v.

The green light on the charger stays on and it never gets to 54.6v, the charger's rated voltage.

I test for voltage with the two "gold" terminals jumped correctly.

I was told by the seller, that this is normal and that the cells just need to balance. If true should I balance on the charger, off the charger, or Just use it (drain it a normal amount) and subsequent charge cycles will fix it?

Any thoughts? Thanks.

 

[taserface]

Have you tried using it yet? Any issues w/ elevated voltage sag, etc? How long after charging did you measure the 53.9v? Minutes/hours/etc? +IIRC, a BMS with passive balancing can take a ~week to settle.

You are charging indoors, correct? (not like in a cold garage, etc)

You're missing ~5% of your capacity, which seems a bit high for a new battery (to me, but I don't know how common that may be, even if I've never seen it that far off after a first charge)... but I think the usual guidance is to drain a decent amount of the battery -> charge to 100% -> leave it connected to the charger at 100% for a few+ hours -> repeat this like ~3x.

 

[vext]

Have you tried using it yet? Any issues w/ elevated voltage sag, etc? How long after charging did you measure the 53.9v? Minutes/hours/etc? +IIRC, a BMS with passive balancing can take a ~week to settle.

You are charging indoors, correct? (not like in a cold garage, etc)

You're missing ~5% of your capacity, which seems a bit high for a new battery (to me, but I don't know how common that may be, even if I've never seen it that far off after a first charge)... but I think the usual guidance is to drain a decent amount of the battery -> charge to 100% -> leave it connected to the charger at 100% for a few+ hours -> repeat this like ~3x.

I ran it down during a ride to like 75% today, charged again and got it to the same 53.9v rather than the 54.6.

If I test while on the charger I get 54.6v so I'm guessing the charger is at least putting out the correct float.

Garage not cold.

I reset the charger by unplugging and letting the LED go off and will see if that maybe fixed it?

 

[urastus]

my initial thought was that it could be one of the cells - but 18650's are 3.7v, so no. I don't know much but I think .7v is closer to 1% - .546v would be 1%. Taserface's recommendation of leaving it on the charger for a few hours after reaching full charge sounds good. Apparently the balancing process continues during this extra time. I came across this video when I was researching e unicycle battery charging. I don't know if they use the same type of bms (or if that even matters) - e unicycle uses passive bms

 

[taserface]

my initial thought was that it could be one of the cells - but 18650's are 3.7v, so no. I don't know much but I think .7v is closer to 1% - .546v would be 1%. It could be that the pack has aged a bit before you bought it? Or the bms?

That assumes the cutoff voltage is 0 volts. I would not suggest that .

3.7v listed nominal, but 4.2 at full charge
54.6v is 13 (*4.2) fully charged 18650s in series
Cutoff voltage is probably closer to 2.9v (or higher) or a 1.3v drop (or lower).

((4.2 max charge - (53.9v measured charge/13 cells)) / 1.3v usable voltage range) = 4.14% drop

 

[Waynemarlow]

a BMS with passive balancing can take a ~week to settle.

More like "many weeks" and many charges.

You need to use and charge this battery at least 20 times before getting wound up by a very small amount of W'hs that potentially you will never ever need. Remember that the 0.03V across 13 cells that you are withering about is the top float charge which holds almost no power.

If you are in further doubt then you will need to at least take the covers off and measure each groups voltage, without that we are just guessing. Beyond that, just send it back and ask for a replacement.