Originally Posted by
philehidiot
A lot of the time there's a chip in the battery pack which identifies it as "genuine" and also kills it dead when the chip decides its days are done.
If it doesn't, you'll probably find it's a bunch of 18650s in there stuck together which means you can relatively easily make your own pack as long as you don't mind a battery encased entirely in duct tape.
Just remember that batteries are an insanely expensive way of dealin' out the pixies. Given the number of charge cycles that's >£10 per KW/h.