My 10 year old Bosch PSR 7,2 has only had light use, and is still in good condition, but the battery is pretty shot. I can get an unbranded replacement, with twice the capacity, from ebay for GBP25.49.
Currently on offer at B&Q is
A Bosch PSR 14.4 V driver, complete with two batteries, for only GBP49.98
Much as I dislike throwing away working kit, I can't really justify buying a replacement battery, could you?
Chris