How Long Will Batteries Hold Charge

I think they will, unless there's a draw on them that you're not aware of.

When I store my boat with the batteries in place, for 5 months the diesel cranks right up.

As someone else said, the best way for long term storage is just to remove the cable from the negative post. I leave a vehicle sitting out doors all winter in Maine and it always cranks right up in the spring. A totally disconnected but fully charged battery will only loose 1 to 2 percent of its charge per month when stored. There can be more than one "phantom" drain if a battery isn't totally disconnected. Lots of electronics and sensors can make small demands that add up over a long time.

It's unlikely the engine batteries will survive. The disconnect switch often doesn't disconnect the ECM. If the disconnect on the house batteries really disconnects everything, mine does, then they should be okay.

We have a 2004 H/Rambler. If you think the engine might not start you could use the Boost switch and try to start the generator; It's only about 15 HP. If the genny starts then you can use the boost switch to start the engine. To do that, let the genny run for sveral minutes then hold the boost switch down for a minute or so. Do that sveral times (with the ingnition key off) then try to start the engine. If you must use jumper cables, use them to start the genny, it takes less current to start than the engine. If your coach is like mine the genny starts from the house batteries, not the engine batteries.

August,

I do (or did before the depression) boat work. When a boat is winterized, it the owner can't take the batteries home, we disconnect (I mean really disconnect them) for the winter. Usually there is enough charge remaining in the main engine battery in the spring to crank the engine. But, we are always ready with a back up and cables.

Matt

Too many variables to take a guess.

I wouldn't count on it. Pretty close to time to self discharge.

If you physically disconnected the terminals then yes. Using the disconnect switches not so sure. Sometimes there are loads that the disconnect switches do not isolate and will drain a battery given enough time.