I thought batteries were reprocessed now, not simply disposed of. I don't think disposal is legal.
As far as being in an accident and the batteries leaking, aren't they glass mat batteries to stop leakage, and in addition the battery compartment is as safe as the petrol tank, so they shouldn't be affected any more than that.
How would you fancy petrol leaking all over the road? I know which I'd prefer.
I'm not a particularly big fan of hybrid and especially not petrol ones, but I'd possibly buy a diesel one.