This is probably too much information, but here it is anyway
I received Battery #1 in early Dec. It tested out at around 70 AH. I contacted Jim at GlobalPower and he sent out another one. Kudos to Jim for good customer service. This one tested at about 80 ah. I didn't want to open them up and void the warranty so I contacted Jim & he said go ahead. I balanced #2 and got it up to 95 ah & I don't think I did a perfect job of balancing so I thought that was good enough.
Now I had some time to tackle #1. Here's a summary:
All the balancing is done through the BMS connector, so no big cable, low voltage drop connection like what is recommended. Since the juice is going thru the little BMS wires & no access to the cell, I didn't really know what the voltage was at the cell when there is current flowing.
The BMS started cutting out (over volt cutoff) at about 13.64V
The cells measured:
There was a delay from disconnecting power to measuring so the high cell wasn't at 3.65 anymore. I've probed the pins while at the limit and it does look like the BMS cuts out at 3.65.
Discharge #2
Since it took so long to balance batt #1 I decided to bleed some off from the high cell this time, thinking maybe that would go quicker. Not sure it it helped.
I found a long section of wire that measured about 0.5 ohms. I tried to run the current thru my DVM, but the internal resistance of that was too much, I only had a trickle of current. I managed to kluge together something that gave me about a 2.7 amp load (measured with a clamp meter). I discharged that cell until the voltage was down to about 3.0 V with the load (probably not very accurate due to the voltage drop). I put it back together and charged it up, but it still cut out at about the same. Did the same thing again, improved my kluge and ran it longer and pulled about 10 ah out.
I put it back together and charged it up (~5ah) & now got it to go to 13.75 before it started cutting out.
Cell voltages: 3.348 3.352 3.360 3.610
So it looks like I took too much out of Cell#2 and now #4 is the high one.
Charge #1
Starting with the lowest, #1, I slowly brought it up. I added about 32.3 AH, with the final measurement at 3.60V, 0.18 amps. There was quite a bit of voltage drop in my leads from the power supply to the clips near the BMS connector so during the day I would set the power supply to 3.68 - 3.75, and monitor the volts near the BMS connector and keep it less than 3.65. It took about 24 hours and I moved on to the next one. It was still taking about 0.25 amps at 3.65.
3.60 3.35 3.30 3.35
Charge #3
A half of a day and overnight brought #3 up to 3.60 & 0.043 amps
3.379 3.351 3.60 3.364
Put the charger on the whole battery until cutoff at 14.0
3.39 3.344 3.645 3.63
Topping off #2
About 3 hrs, 3.3 ah, brought it to 0.02 amps at 3.61
Top off #1 (again)
About 1 hr, 0.53 ah
After sitting for a couple of hours the cell voltages were:
3.443 3.526 3.446 3.373
It seems curious that C#4 is so low.
A discharge test showed a little over 100 ah. I didn't have a shunt or battery monitor, the capacity was estimated with lots of amp measurements, and a pretty consistent load.
After the discharge I was able to charge it up to 14.2 V before it would cutout.
Cell volts: 3.493 3.639 3.633 3.464
Not perfect, but good enough.
