NiMh power tool batteries are less prone to the memory effect. In fact many tool manufactures will tell you that their cordless drill is completely free from this effect. This is somewhat true. Memory effect is more common in low drain devices like cordless phones. A cordless drill draws a lot of power, and in bursts.
Modern batteries suffer a lot less from memory effect. Nevertheless batteries in cordless drills still lose their ability to power the tool. It might not be the memory effect but due to the chemical reaction taking place inside the battery every time you charge and discharge it.
Newer Nickel based batteries might be less prone to memory effect but they do suffer from “crystalline formation.”
Crystalline formation refers to the condition when crystals form on the anode and cathode inside the Dewalt power tool battery, reducing the surface that comes in contact with the electrolyte. This can severely reduce the current flowing between the terminals of the battery and hence its effective power.
Crystalline formation occurs over the normal life of the battery but happens a lot faster when the battery is overcharged or charged repeatedly without allowing it to discharge completely.
Severe crystalline formation can result in the larger and sharper edges of the crystals causing permanent damage to the cell inside, facilitating rapid discharges and irreversible malfunction of the battery.
“A battery that hasn’t been reconditioned in over one month may begin to show effects of crystalline formation. After five months there will be a noticeable degradation in battery performance. After six months there might be permanent and irreversible damage inside your cordless drill battery.”
So its good to recondition your Nickel drill battery once in 30-45 days. Reconditioning requires the battery to be completely discharged to a voltage of 1V per cell. This kind of discharge is the most easily performed by following the deep discharge method described above for removing memory effect.
Battery reconditioning devices are available in the market for reasonable prices. If you can find one, a reconditioning charger is a good investment if you use cordless drills and other battery powered tools.
Check your user manual. The charger that came with your drill may already have the reconditioning function in it. Many modern tools come with the guideline that “its okay to leave the battery in the charger when not using it.” This is because the charger takes the battery through the proper reconditioning and maintenance cycle when required.
If none of these methods are possible perform the “deep discharge” like we mentioned under reconditioning of memory effect.
Caution: Do not perform manual deep discharges too often. It also causes stress to a healthy power tool battery for Panasonic.