Ordinary batteries produce energy from a
chemical reaction. Rechargeable
batteries
work on the same principle, but
unlike ordinary
batteries, the chemical reaction
can be run
in both directions so that they
can repeatedly
store electrical energy during
charging and
deliver it while discharging.
Not all rechargeable
batteries are alike, however,
so when shopping
for a rechargeable battery, consider
these
common alternatives:
- Nickel cadmium (NiCad) batteries were the first rechargeable batteries. They
come in all of the common sizes of ordinary
batteries and have the lowest purchase price.
Generally, you may charge and discharge a
NiCad battery hundreds or even thousands
of times, but these batteries have a tendency
if not fully discharged to become unable
to hold their original charge. The partially
depleted capacity becomes their full capacity
in a phenomenon known as memory, but they
can recover if fully discharged and recharged
a couple of times. They tend to lose power
even when not in use and so fully discharge
in a month or so, depending on the battery.
Nevertheless, the total cost of ownership
for NiCad batteries can be dramatically lower
than ordinary batteries for demanding applications
like digital cameras.
- Nickel metal hydride (NiMH) batteries do not suffer the memory problems of nickel
cadmium and are generally lighter for the
same amount of power. Like NiCad, NiMH batteries
come in all of the standard sizes and have
a similar, though improved, shortcoming in
shelf life. NiMH batteries may not be a suitable
substitute for NiCad in high drain products
like power tools, but in every other application,
they will generally perform better at a somewhat
higher price.
- Lithium ion batteries improve upon nickel metal hydride with even
more power in a lighter package and will
hold their charge for months without appreciable
loss. Lithium ion batteries power top of
the line notebook personal computers. Their
current disadvantages are their higher price
and their limited use (they are not available
in ordinary sizes because of the complexities
that require that they be recharged in specially
designed chargers).
No matter which technology you
choose, a
rechargeable battery eventually
loses its
ability to take and then deliver
a full charge.
Once the capacity begins falling
significantly,
it is time to replace it. |
