Thanks everyone. Just a few comments in response, the hot water heater wasn't on at the time, I will have someone (I am not at camp today) check the emergency brake to make sure it wasn't pulled out accidentally, and I know both batteries were full of water when I started the season a few weeks ago (I had one that got low a few years ago and almost started a fire because it got so hot when it was charging, luckily I could smell it before it did anything).
Unfortunately I am beginning to think that your right in that the batteries are just getting old and aren't holding a charge. That's a very very bad thing, not because it means I have to buy new batteries but because it means that my wife was right in that I should have gone and bought a new battery yesterday before I left camp and now I will never live that one down :)
However, I've always held off switching to a 6 volt system because I was buying batteries at different times but if they both need to be replaced maybe now is the time to switch over. Are the 6 volt systems really that much better?
Thanks Everyone.