You’ve probably heard term “Memory Effect”. “Memory Effect is the phenomenon that makes a cordless drill battery lose its capacity to deliver a full charge. It happens more with NiCd batteries much less with NiMh and none whatsoever with Li-ion. In other words only the Nickel based batteries (Ni) suffer from memory effect.”
When a battery is repeatedly partially discharged, it only remembers the last amount of charge it held. If more power is demanded the next time, it shuts down completely as if to protest against the extra work. That in short is the memory effect.
The simplest way to remove a memory effect from a cordless drill is to make it go through a reconditioning charge cycle.
In order to do this:
Charge the drill fully.
Discharge it completely under zero load, i.e. allow the drill to run on its own till it stops. People usually accomplish this by taping the trigger in an ON position.
Charge the battery fully again.
If this procedure improves the performance of the battery then repeat it only after at least one month.
Caution: Do not try this with a power tool battery for Makita that’s working properly already. You should charge a normally functioning battery whenever it loses substantial power to function. Do the deep discharge described above only when you are trying to recondition a battery that doesn’t work properly anymore.
Important Note: Check the user manual of the cordless drill. Your charger may be equipped with the ability to deep charge/ recondition the battery. Follow the instructions, if any, before you try this.
If this doesn’t work, it may be time to buy a new cordless drill battery for Hitachi.