First, 12 V batteries are never wired in series (except in the rare 24 V system). The connection is always in parallel.
If you have connected the batteries in series and they are 12 V batteries, the circuits have been seeing 24 V, this is not a good thing. You would expect that there are fuses and/or circuit breakers faulted. Damage to other devices may occur.
I'm a big advocate for DIY but I think your basic lack of knowledge is starting to hurt you in this case. I would suggest you hire someone to look over your 12 V system. That someone would not be the guy at Autozone. I'd suggest an RV service garage and please, disclose to the folks there what you've done to make everything work, even what didn't work.