Battery capacity refers to the amount of power that an electric battery is capable of holding. This term is often used in association with rechargeable batteries, as due to the strange memory effect that older types of batteries exhibit, they will not hold as much power over time unless they are drained before they are recharged.
Nickel Cadmium batteries are the most traditional of the electric batteries of modern day. These are the batteries that are notorious for suffering from the memory effect. If you constantly recharge a nickel cadmium battery when it is nearly full you will soon find yourself having to charge the battery more than you’re using the power it’s built up.
The memory effect seems to work as though whatever the power level of the battery in question when it goes into the battery charger, it sort of ‘resets’ it’s memory in such a way that the given amount becomes zero, or no power to the battery. It will never be able to put more charge into the space that it considers to fall outside of that new range.
Some people think that nickel metal hydride batteries do not suffer from the memory effect at all, where others swear they have noticed a memory effect, though not as pronounced as with more traditional nickel cadmium batteries.
There are two much newer battery types that successfully avoid the memory effect issue altogether. The lithium ion and the lithium polymer batteries can be recharged at any point and will never have decreased battery capacity.
So make your choices wisely. These main battery types are found in everything from double A’s to laptop batteries and cell phone batteries. Regardless of the application, the different types have these advantages and disadvantages mentioned above.
If you can afford the new Lithium batteries, go for it. You will spend less time recharging items that run on lithium batteries. And lithium batteries will last longer overall. But if you don’t use these items very frequently it may not be worth the higher price.