From powering cordless telephones to remote-controlled cars, rechargeable batteries are found in a variety of electronics. As Nickel-Cadmium (NiCad) and Nickel-Metal Hydride (NiMH) batteries age, the cells inside of the batteries tend to not hold a full charge. Old rechargeable batteries still have some life in them, but the key is to charge them properly using a charger designed for rechargeable batteries. Your older rechargeable batteries are easy to charge, so the batteries can provide years of service.
Purchase a New Recharging Unit
Replace your rechargeable batteries' old recharging unit with a new one. Modern units recharge a variety of battery types, and they are specially designed for rechargeable batteries. The recharging units also have built-in controls that keep your rechargeable batteries from overcharging and exploding, developing a "memory effect" that keeps the batteries from reaching their full charge capacity.
"Top Off" Instead of Draining the Batteries
"Top off" your old rechargeable batteries by placing them in the charger immediately after using the batteries. Do not wait until the batteries completely drain. The sooner you recharge the batteries, the more recharge cycles you will get out of the batteries.
Store Your Old Batteries Properly
Do not leave your old rechargeable batteries in a device, including a flashlight, smoke detector, digital camera or other device, as this will cause the batteries to discharge. Also, do not toss the batteries in a drawer or a box. This will cause them to self-discharge. Remove the batteries and place them in a modern recharging unit that offers protection to keep the batteries from overcharging.
Let the Old Batteries Cool
If you recently used the device containing old rechargeable batteries and the batteries are NiCad, then let the batteries cool before placing them in the recharging unit. The recharging unit can be fooled by the warm battery and not charge it properly. Let the NiCad batteries cool to room temperature before placing them in the recharging unit.
High-Capacity Older Rechargeable Batteries
If your older rechargeable batteries are labelled "High Capacity," then most chargers won't be able to fully charge the batteries. Still, recharge the batteries after each use and do not wait until the batteries are totally drained before recharging them.
Mixing Batteries in the Recharging Unit
If your recharging unit charges batteries in pairs, do not charge NiMH and NiCad batteries at the same time. Look at the side of your old battery for the type of rechargeable battery it is, and charge similar types together. Also, charge similar capacities together, such as 2100mAh and 2200 mAH. Charging different battery types and capacities will cause the batteries not to charge fully, depleting the batteries over time.