Stupid answer here, but here I go... Are you sure the charger isn't dead itself? I take it you tried other chargers to use on the phones. If that's the case then it will be the battery could be damaged or very very rare the circuit board got damaged from too much output if it was higher then the original charger. Take my answer with a grain of salt as its only a wild suggestion. But hopefully it was the actual charger that is damaged. Do try the original chargers again tho