How Batteries Are Measured
There are a few different ways to 'measure' batteries, here
are the ones I will be comparing
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 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 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'.
Some batteries are rechargable, usually they can be recharged 100's of