NiMh doesn’t mind being completely discharged, so they should charge up again. If they’ve gone completely completely flat though, sometimes the charger doesn’t recognise them because the voltage is too low. There is a little trick you can do to fool the charger into starting a charge but I cannot for the life of me remember how to do it. It can be done.
Find a good battery and parallel them up with coins / screwdrivers / whatever metal you have handy, outside of the charger. Hold for a few minutes and then stick the old battery straight in the charger.
NiMh doesn’t mind being completely discharged, so they should charge up again. If they’ve gone completely completely flat though, sometimes the charger doesn’t recognise them because the voltage is too low. There is a little trick you can do to fool the charger into starting a charge but I cannot for the life of me remember how to do it. It can be done.