Did you look inside the old battery? It may well be just a bunch of 18650 cells with some electronics in a plastic case. Just desolder the old cells and solder on new ones.
I did the same for my wife's cordless vacuum, and it works better than new, because the new cells are about 2x the capacity of the originals.
I did the same for my wife's cordless vacuum, and it works better than new, because the new cells are about 2x the capacity of the originals.