When we hired from Bruce Boats on the K&A it was a requirement to run the engine a certain number of hours a day - and be responsible for any battery damage if you didn't. Mind, these were fully disabled accessible with motorised lifts front and back, charging points for Powerchairs and the like. I was having a gentle "nose" (as you do out of curiosity) at the 240v, 24v and twin 12v electrical systems and found a neat rack of USB data loggers - presumably Bruce Boats had been caught often enough in a "yes we did", "no you didn't" for it to be worthwhile being able to prove "look, Tuesday you didn't start the engine until 10:00 and stopped at 13:00"