How can you tell when a ni-mh rechargeable battery has gone bad?

A Ni-MH rechargeable battery may indicate it's gone bad if it shows significantly reduced capacity, failing to hold a charge or only providing power for a short duration. Additionally, if the battery becomes excessively hot during charging or discharging, or if there are visible signs of leakage or swelling, these are clear signs of failure. Finally, if the battery voltage drops well below its rated capacity, it is likely no longer functional.