Weak batteries

[BillG43]

Started coach(DP) December 2, no problem. Came back January 2, batteries weak, won't turn over. Used battery boost, still won't turn over. Batteries new last year. Master kill switch off and coach batteries off, what would be draining these? Shouldn't batteries last longer than one year?

[BFlinn181]

Yes, batteries should last longer than a year, but use and abuse takes a toll. If the batteries are discharged to 12 v or less (50% discharged) a number of times, they will be harmed. If electrolyte is allowed to evaporate and replaced with anything but distilled water they'll be damaged. Dirty connections don't allowed full and efficient use or charging. You didn't mention where you are located, but if in a cold climate you should know that a discharged battery can freeze. A fully charged battery won't be damaged by the cold.

You said you turned off the 'master kill switch.' Is that the battery isolation switch or a physical disconnect switch? On my RV the battery isolation switch doesn't actually do a 100% shut off, LP detector and a few other things still are connected, so I installed knife switches on the battery terminals. On the chassis battery, engine ECU, radio presets, clock are often still connected. You can remove a cable from the battery post if you don't have shut off switches.

["007"]

Welcome Bill to the forum and irv2.
You have not said what coach and model you have but most coach's have a Bird System in them to keep your batteries charged if you have access to 110-120 outlet.
As already described by Bob there are items that will discharge your batteries but the LP Detector has a switch in your display area along with the BDS to cut off the house batteries from controls of appliances.
The coach chassis battery's may have a cut off switch also so ECM & TCM, radio and other items, your steps maybe off chassis battery also.
A small solar panel on roof is suppose to keep chassis batteries charged so the parasitic loads can not drain the chassis batteries, but if coach under cover that would not work.
Here is a link explaining a Bird System and batteries in a DP coach that's fairly new.
If you can give your coach type beside the DP indication can supply more info, plus you will find more links below in my signature that can help you with your coach.
When you used the battery boost did you operate the BDS SWITCH to ON?