[Al Skierkiewicz]

If the battery has been run down to zero volts, the smart chargers will not even try to charge them. Sometimes a simple charger will be able to pass enough current to charge them up to the point that a smart charger can then be used. If you use a simple charger or a bench supply, monitor current. If you cannot get a current flowing they are open internally probably due to a fall at some point in time.