The characteristic of Ni-MH Cell:
A 50% charged cell could able to leave without usage approximately for 5 days until the cell become flat.
The entire cells flatted within a battery pack
The cell will be damaged if it is totally flat (0 Volt) caused non-use status. A charger won’t charge the battery if all of the cells within the battery pack are flatted (0 Volt).
Some of the cells flatted within a battery pack
In some case, the user would still charging their battery by using a charger without notice of one or two batteries has been damaged already within the battery. An explosion will possibly take place. (The charger is non-detectable of one or two cells being damaged within a battery pack)
If the charger continuously charging the battery pack, the damaged cells will be over charged and resulting an explosion.
To prevent the explosion occur, it is essential to take care of the Ni-MH battery.
Tekin Battery Nurse could able to help!
However it is only one of the example, other danger may also occur by using the battery unsafely.