Doing a DIY van conversion and ran into trouble after COVERING the van (yes, I have a very large cover to tuck the van in when we have to take an extended break) but NOT shutting the house electrical system down (I know, dumb).
When we uncovered the van 5 weeks later, van battery was completely dead, FINALLY got it jump started, but now have very weirdly behaving house batteries (lithium). They appear fully charged, but don’t maintain their charge when I turn anything on, unless we also have (a) full sun, (b) van turned on, or (c) shore power plugged in.
We are thinking it is related to the isolator charging the house batteries from the alternator while the solar panels were covered with canvas. (In case it matters, we do NOT have a “smart” isolator.) We assumed that the isolator would stop the draw from the van batteries, but maybe it didn’t? That would explain the van battery being dead, but did it also ruin the lithium house batteries? And how does one figure out if lithium batteries are ruined if they say they are charged 100% but then jump up and down in volts and then stop working as soon as anything is turned on?
It sounds like they are simply dead to me. I’m not an expert on lithiums but a simple test would be to charge them to full with nothing hooked up to them then simply meter them after a few hours. If the voltage is low then they are probably dead. You could have hooked your isolator up backwards, or it could have been backwards.
Even if you do cover it up, you should keep some type of trickle charger or shore power supply hooked up to keep you batteries in good shape.
I’m going to agree with @Bretly here, but add a little to it.
A) Disconnect your charge controller first, then your house battery(s).
B) Fully charge them while disconnected with a lithium compatible smart charger.
C) Troubleshoot your isolator, it probably isn’t working correctly.
Your charge controller needs a battery connected to it, before the solar panels are connected to the system. If you connected the solar panels first you could have killed the controller. With the description of your batteries, they could have killed your controller too. Is your controller even lithium battery compatible.
Without a charging source, almost anything left on, even just the charge controller, could have drained your batteries. It’s a good practice to use low voltage cut offs on both your house batteries, and your starter battery.
Your starting battery may be a totally different problem. It’s not unusual for computerized vehicles to drain their batteries if not used in as little as a couple of days. Some might make it a couple of weeks, but 5 weeks is really pushing your luck. Once again, a low voltage shut off will solve that problem, or a battery disconnect.
Cheers!
"Never gamble more than you can afford to lose." ~ Dare2Dream