If you want to test at higher rates, use a shunt and your inverter for a pack. For individual cells, just hooked up multiple loads and add their measured capacity when done.
I like this idea of using a shunt, but the one I found capable of this is the Victron Smart Shunt, which is about $100 alone or $200 with the meter. I purchased an Ailii shunt recommended to me by a user and I see Will uses these and it is between $20 and $40, but has no data logging capabilities. I can see how many amps I use now on the AiLi, but not how many amp hours expended.
Also neither has a cutoff voltage like a true capacity tester, unless you’re running to the low voltage cutoff of the inverter. If the low voltage cutoff of the inverter is 10 volts, than you match the 12 volt low voltage cutoff of 10 volts. My 12 volt inverter cuts off at 10.5 volts, so a capacity test done this way will not show a full capacity. So, I have no idea what 2.625 is per cell SOC wise, or even if all 4 cells would be balanced at that point, but I do know I can’t take these cells below 2.5 VDC. This also does not provide individual cell data, only groups of 4.
Honestly though, I am not looking forward to spending three weeks charging my 16 eve cells on a 10 amp power supply, and then discharging them at 20 amps, and then recharging them. THat would get me good individual data to group my 16 cells into balanced groups of 8.
I did get the spec sheet for each battery for from China before they shipped. I’m thinking of double checking the by purchasing a $75 battery internal resistance tester and if that checks out, not spend the next three weeks capacity testing. If the internal resistance checks out, then I would just build the packs based off the spec sheet. I would top balance before doing the resistance check.
I capacity tested 11 cells to make an 8 cell 25 ah battery, and I have to say I did not enjoy that at all.
That is three weeks done efficiently with 16 cells, 280 ah each, a 20 amp battery tester that auto cuts off at 2.5, and a power supply that can charge each cell at 10 amps, and since I need to do things like work and sleep, that would easily turn into six weeks.