I agree with drbatts above comments about switching up the batteries or the banks themselves to see if it's the battery specifically. On top of that, as he mentioned, how old are the batteries? Do they have a sticker with the date on them? Batteries can be very funny or quirky, I've got a 2006 Honda Civic as my daily driver that has 250k miles on it. The other day I went out to start it up for work and it wouldn't even turn over. I popped open the hood, hooked up the jump pack to it as well as the charger and couldn't get it to start. Pulled the battery and noticed it was wet underneath and where it looked like it was leaking from the bottom of it. It also had a sticker on the battery that said "01/16", so it was just about 7.5 years old at this point and I'd say I got my money's worth out of it. Took it to Costco and bought a replacement, threw it in the car and it started right up. Not exactly an apples to apples comparison, but getting back on track here and to relate a little bit to the OP's issue... the battery worked just fine until it didn't. I had no issues with it up until about a week and a half ago, the morning I went out to start it up and it wouldn't turn over. Before that, no issues with the battery whatsoever and it would start up just fine. Not sure what happened or why the battery started leaking, but they can and do go bad just from age, lack of use and so on. Especially if you're like me, or others, with my boat where I store it all winter and then start it back up during the late spring/early summer. And that's on something that's been sitting for almost 6 months, whereas a car that I drive everyday should be a little bit better on batteries.
