Single cell or multiple cells in some kind of battery pack or casing?
If it's a single cell and won't recharge, they might be gone if you're sure they were working properly beforehand. If they haven't been charged in awhile and the voltage was allowed to go way low, you might need a smart charger to recondition them but even then they might not recondition.
If it's a pack, dropping might have caused a solder connection to come loose somewhere. Crack the case and have a look.