I have a solar set up with a charge controller and a single 12v deep cycle battery. After taking the set up on a trip once, we realized the battery had a much lower capacity than we calculated. We took it to a battery shop and they tested it, and confirmed it was defective. We got a new one from them, and they showed that their tester confirmed it was like-new. I thought my problems were solved.
I hooked it up to the solar set up. We have not had time to use our full load on it yet, but it seems like it is draining itself too much. Today was a sunny day, and the charge controller reported that the battery was fully charged (5 bars, I didn't look at the volts at that time). Before the sun even fully went down, the battery had dropped to 3 bars. I checked the voltage, it was around 13.2 volts.
I thought that maybe the charge controller or the inverter were draining from it, so I disconnected both of those. I checked the voltage again (10 mins later), and it had dropped to 13.17 V. I disconnected all wires from it, and it is just sitting in my garage now, and it is draining about 0.01-0.02 volts per 10 minutes.
This seems like *way* too much. Some quick googling showed that lead acid batteries drain 5% per month. Assuming that 5% is of total voltage, not usable voltage, that would mean (0.6 V per month). At the rate this is going, it will drain that in 6-12 hours.
Did I somehow get unlucky and get a bad battery again? Or is it that my charge controller is over charging the batteries and damaging them? Could that damage happen in just 2 days?
FYI here is my charge controller: https://smile.amazon.com/EPEVER-Cont...dp/B015XAB7M6/
And I have a 30 A breaker between the charge controller and the battery. The battery is a 12V 80 Amp Hour lead acid battery.