GHA
Well-known member
Good writeup here, he found the same inaccuracies during charging > https://marinehowto.com/smartgauge-battery-monitoring-unit/Absolute battery capacity isn't relevant as it only reports a percentage result. So 60% doesn't mean 300Ah left in a 500Ah bank. It just means 60% of whatever capacity your batteries can store. Older 500Ah bank might only manage 400Ah and it would be 60% of that figure.
Hardcore Plans afoot here to hopefully build an arduino based constant current load which will let the house loads stay on and log all the data, might work, might not.. gold dust if it does to keep track of capacity, even if it's just relative.I actually did carry out tests on my previous set of batteries and it was very labour intensive over 4 days. I monitored Voltage, Amps load, SG and temperature hourly from very early in the morning for about 18 hours each day.
Temperature control wasn't a big deal as I stuck each battery in a big water bath overnight before testing and during the test. I don't think temp. varied by more than a degree C at most.
Load control was a bigger problem but I did manage reasonably well with a variety of small bulbs and a larger one. I noted actual current and included that in the final calculations so that Ah wouldn't be far off.