If the batteries have been left totaly drained for to long, they are dead. To long is anything longer a day.
This hold for ALL Li-ion or Li-MH batteries.
If left unused for several months, they will slowly loose their charge. After about 6 months, the remaining charge become criticaly low. You must put them back in the charger.
If it's a Ni-Cd battery, it needs to be totaly discharged before you recharge because of it's memory. Those can be left drained.
Electro
May 2013