How Batteries Are Measured
There are a few different ways to 'measure' batteries, here
are the ones I will be comparing
Size
This is pretty straight forward, how big are the batteries? Lead acid
batteries don't get much smaller than C-cell batteries. Coin cells don't
get much larger than a quarter. There are also standard sizes, such as AA
and 9V which may be desirable.
Weight and power density
This is a performance issue: higher quality (and more expensive) batteries
will have a higher power density. If weight is an important part of your
project, you will want to go with a lighter, high-density battery. Often
this is expressed in Watts-hours per Kilogram.
Price
Price is pretty much proportional to power-density (you pay more for
higher density) and proportional to power capacity (you pay more for more
capacity). The more power you want in a smaller, lighter package the more
you will have to pay.
Voltage
The
voltage of a battery cell is determined by the chemistry used inside. For
example, all Alkaline cells are 1.5V, all lead-acid's are 2V, and lithiums
are 3V. Batteries can be made of multiple cells, so for example, you'll
rarely see a 2V lead-acid battery. Usually they are connected together
inside to make a 6V, 12V or 24V battery. Likewise, most electronics use
multiple alkalines to generate the voltage they need to run.
Don't forget that voltage is a 'nominal' measurement, a
"1.5V" AA battery actually starts out at 1.6V and then quickly
drops down to 1.5 and then slowly drifts down to 1.0V at which point the
battery is considered 'dead'.
Re-usability
Some batteries are rechargable, usually they can be recharged 100's of
times.