I realize this is an older thread, but thought I'd post this here anyway. This is copied from a post I made in the Valence super thread.
Hi all, I'm trying to work out what the capacity of my 2 u27-12xp batteries is. I was hoping someone might be able to check my method for testing them. I have the 2 modules wired in parallel, and am testing them by running a space heater off of a renogy 2000w inverter/charger. I am measuring the current using a victron BMV 712. I have the space heater set on low which pulls about 775 watts as measured by the shunt. My method for assuming that the SOC is at 100% is basically just waiting for the charger to decide to stop charging. Once the charger has stopped its charging cycle, I check the cell voltage using a thunderstruck vc1. The highest resting voltage I've seen so far is about 3.4v/cell. I begin the test there and end it when I hit 3v/cell. When the test is over (which I must be doing wrong) the BMV reads that 182 amps have been used. Thats 65% of the capacity I should be getting! I realize these are used batteries, and probably won't deliver the full 138ah/module anymore, but that seems super low! Can anyone show me where I've gone wrong/how you should do a proper capacity test? Is my charger not charging them all the way up? The ebay seller says they should have >90% of life span on them still.