Are your Game Boy sessions slowly falling from two hours to a half hour on a charge? Is your PSP unable to make it through a single movie? If you use a cell phone or a handheld gaming system, knowing what type of rechargeable battery it has and how to charge it will prolong the life of your battery, lead to longer charges, and save the planet a little. Every battery should state what type of chemical it uses to store its electrical charge as well as the voltage in volts (V) and amperage in milliamps (mA).

Quicktip: - All batteries perform better when warm (not hot). If a battery is on low power - like a car battery - warming it with a hairdryer may help.

Choosing a Rechargeable
Check the package for amperage. A AA battery rated for 2500mA will last longer than a 1800mA battery, regardless of brand (though brand does factor with traditional alkalines). If you are buying a replacement battery for a phone, you can pick ANY battery that has the same voltage rating, get a higher mA rating, and have longer talk time. Note also that most cordless phone batteries are regular AAA or AA batteries vacuum-sealed; so you can probably put together your own replacement if the original battery has died.

NiCad - Nickle Cadmium - These batteries have what is called, "memory." In order to preserve their life, you should let them completely discharge before charging them again, and you should charge them in a "slow charger," or one that takes 12 to 24 hours to charge. Charging a NiCad battery before it completely discharges, or worse, leaving it on the charger will shorten the battery life. NiCad is cheap, but heavy and with a short life.

NiMH - Nickle Metal Hydride - These batteries have no "memory" (in theory), and can therefore be left on the charger. They can be charged quickly, and store more energy than an equivalently sized NiCad battery. NiMH is the most common and highest-value battery. However, in practice it is still best to fully-discharge the battery before recharging. It will extend the life of the battery.

LiIon - Lithium Ion - Camera batteries; expensive, but they hold significantly more charge than a NiMH battery, and definitely have no memory. It is lighter and holds more charge than a NiMH (which is why most all laptops have LiIon batteries). Leave it on the charger, or don't; LiIon is easy.

Lead-Acid - These are the batteries in your car. There are two types available: starting and deep-cycling. Starting batteries are meant for starting; if you completely deplete the battery it will never hold its charge as well again, and will degrade more rapidly. Deep-cycling batteries are similar, but able to be discharged for long periods of time as well, making them generally more durable, and therefore much more expensive. Lead-acid batteries perform poorly in sub-zero temperatures.

Final Note
All batteries eventually die (no longer able to hold a charge). However, rechargeable batteries are always more cost-effective and environmentally-friendly than their disposable peers.