Doesnt really apply to the problem.....but ive found this....
I had to buy a new battery for my merc some months back....coz it was parked up waiting for some bodywork repairs.....it didnt move or get started for weeks.
I think the prob was the alarm flattened the battery and it was left with a flat battery for some time.
It wouldnt recharge.....well it would....it would start the car once.....then couldnt after you switched off.
I think the answer is...if the car is going to left for sometime (like a couple weeks or more)
if parked outside on driveway and near enuf ..... shove a battery charger on it....set to trickle charge.
Or if left at airport/etc for a period of time.....is to get one of those solar panel trickle chargers.....the ones where you shove the solar panel on the dash board......plug it into the ciggie lighter.....and then hopefully when you come back from abroad all tanned....your car will start and not have a flat battery