You should probably discharge it below 0V.
Let me explain. If it is in a pack of 4 batteries, and one is weaker, than that gets to 0V first. Then the device still discharges them, than that weak cell goes into something called cell reversal. At least, thats what they call it with Li-ion batteries. I'm almost sure that this is causing the leak, and not the discharge.
You know, what they always say... Dont turn it on Dont mix batteries, use a fresh pack.