So the bewitching hour has struck, and the capacity test continues on.
Testing high capacity batteries takes a lot of time. Note to self for future tests: Start earlier in the day!
The 60AH battery has been under a 6 amp (C/10) load for 10 hrs 15 min and the voltage remains at 12.47 V. I have the test termination defined as 12.00 V, a value substantially higher than the theoretical cutoff point. In fact for a unbalanced 4-cell battery the recommended cutoff would be 11.2 volts and for a controlled discharge even lower.
Bottom line is the battery capacity will probably work out to be closer to 65 AH.
