Matt, even with the switch off most Electronics have a small drain. In RC cars it's stuff like keeping some of the FETs awake and these days the capacitors charged.
You have to face it that your batteries are probably damaged.
If any of the cells are 'puffed' it's time for disposal.
I've once before revived a Li-Po pack (from a aeroplane that got stuck in a tree for 4 days). I used a Ni-Mh charge profile to get enough voltage in (at reasonable current, somehing like 1A I think) just to give enough voltage that Li-Po profile could recognise the cells.
Please do this outside, don't leave it un-attended and keep a bucket of saltwater an an extinguisher at the ready! (insert other disclaimers here)
For what it's worth the cells were revived but were never as good for runtime or voltage ever again, and had a much shorter life thereafter than an identical pack that didn't get stuck in a tree.
HTH,
Chris.
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