you can also use a hgh current AC adapter, 120 V in 13V out in whatever
current rating you want.advantage of this is having a handy 12 volt
source for other uses, even a car battery charger should do. if its
current capacity isnt enough the worst that can happen is a drill with
less power

have a friend who tears apart battery packs and replaces just the
cells, which he has found are always regular rechargeable batteries.
cheaper alternative if your handy and dont mind slodering wires.

Its sad so much is disposable today, battery pack could easily be made
to accept new rechargeable batteries