If they are after market chargers then they are probably not putting out the proper voltage... if they are proper chargers it could be the wall plug is reverse polarity... a 5 dollar wall plug tester which looks like a mini charger and bought at any local hardware store can tell you that with its 3 light system.... be surprised how many are wrong in a house.. if that isn't it the charger maybe shot... unlikely two different chargers are bad though... more likely a second hand pad with dead batteries... which means a trip to the repair Depot. But if they are stolen ...