hi,,i have a 52 plate cooper s,, pulled the boot carpet back which feels dry on top to find the battery sitting in an inch of water and the top of battery wet and around battery well wet,,i would never have come across this as the carpet in boot feel dry,,any help?,steve

Might be a leaking seam where the battery box it fitted into the floor?
Sure it is water? and not from the battery itself?
Pull the battery out and have good look around, if it is water theres normally a telltale track where its coming from?
Does the battery box have a drain hole in the bottom?

Hi, I have exactly the same issue, and the battery voltage was too low to start the car today!

I've cleaned it all up and charging the batter as we speak but never had this issue before now, I know it's been wet in the UK but I can't figure out where the water is coming in from... If you get anywhere please let me know!!! Mines an '06 cooper s with quite a few mods but nothing that touched the rear of the car...

It often comes from a failed seal around the high level brake light which finds its way down the rear hatch/boot. Fold down the seats climb in the back and get someone to direct a hose at the rear hatch area while you watch for leaks. Also check rear light seals are not leaking inside and wiper spindle.

this happened to my friends mini, and iv heard its a really common fault, he discovered water filled about an inch off his battery terminals, it was the seal around his boot that was leaking but he just drilled a drain hole, not the best solution though i must admit