First of all, no I would never attempt anything with the batteries. Way beyond me!!
No danger at all of that!!
The reason I question if there may be an underlying problem with the batteries:
1. Nov 2014 purchased rig (2006 Winn Vectra) and were told batteries had been replaced there over the summer. Can't verify that as we failed miserably on checking things out before we purchased! Our first and biggest mistake of all!
2. Dec 2014 - can't recall all the problems we were having without my notes but were told batteries were bad and replaced all three Here again, our ignorance. We said okay, asking no questions as to what type we should get etc. (Yes we have learned a heap the hard way!) so they did three 12 volt Interstate Marine/RV SRM 29 deep cycles which we have learned since are not true deep cycle as they are combo and have cranking amps. We go on our way and the new batteries did correct some issues.
3. From that point we occupied the MH for part of December 2014 on shore power and then in dry storage till March 2015 in Arizona.
4. Upon return in March everything was dead. We had turned off everything but forgot to do the battery disconnect. Got it charged, and then occupied mh thru April before storing again near Sedona AZ for the summer in dry storage in shade but yes it's az so it's hot This time we did do the battery disconnect.
5. Returned mid October 2015 and stayed in park on shore power till mid December.
6. Next was a big mistake. Left in hurry early morning to get to a flight. For some reason I do not recall we disconnected from shore power with intention of also disconnecting battery, but that tiny little detail
was lost in our hurry. So of course the battery went dead while we were gone.
7. Jan-early April 2016. Traveling Arizona and Southern California and also couple of appointments at RV repair for other issues etc. Mostly shore power but also did some dry camping. Charging 3ish hours morning and evening would leave us at 12.0/11.8 by morning/evening and having used very little power meanwhile. Used propane water heater and only turned on when needed, zero tv, very little lights using oil lamp for most of light, no heat, etc. there's a thread on that etc. basically using very little power and cycling deeper than we should even at twice a day. Maybe that was because we never got a complete charge as I understand it takes longer than three hours. Btw I estimate total dry camping to have been three weeks spread at various times Anyway...
8. In this time period we were checking water in batteries and doing that maintenance. Water was never too low to our knowledge.
9. At some point during above time - January - hubby did check and found one battery to be bad. Took it in, confirmed, and decided ok it was a case of one dragging the others as far as efficiency so decided to see how well we did with two good ones and just removed the bad one. (Two months out of one year warranty of course) We also weren't ready to replace all three, the other alternative. Mechanic said good idea to try with two good ones. Turns out that made no noticeable difference.
10. In March another battery check by hubby showed now the other two batteries to be bad. Since he was going to be leaving and I would be on shore power after that we decided to make decisions on battery replacement when we return in the fall.
Bottom line - we know replacement is necessary but before we make that investment and decide on type (not room for golf cart type), etc we want to be sure there's not something else causing batteries to go bad.
I have outlined the complete history with our batteries. Yes they have been cycled deeper than they should be when dry camping a total of no more than three to four weeks and yes we have made a couple mistakes on running them down completely and yes they were in az heat for a summer. Question - is that enough abuse to warrant these batteries being completely bad this soon? If not, what should we be looking at in finding a source of the problem?
Last repair place insisted there was no problem with what were at that time the good batteries, that I was worrying about nothing, and to prove it they proceeded to do a test and leave lights on at battery power for several hours, cycling them very deep in the process to around 11.5. He missed my point. I wasn't trying to see just how deep we could cycle. Thanks to wonderful info and diagnostics about the inverter issue by Sky Boss I now understand the inverter issue and can operate things with confidence and with no more problems!! That's where I need to get with the battery topic. I need to either confirm there is likely a problem OR understand the limitations and live with it. No mechanic has been able to come close to getting me there.
Now I'm off topic and far too wordy as usual but so emboldened by progress otherwise that I have to ask in this setting for anyone with enough patience to follow it!