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Re: Batteries

> kilomockingbirds; but I still don't know a correspondence between cranking
> amps and amp-hour ratings.  Is there one?  It seems that aircraft batteries
> are mostly rated in Amp-hrs (AH), and the auto batteries (including the
> group 70 battery I'm considering buying) in cranking Amps.  Also, the guys

I'm not sure what a group 70 battery is, but here is the take on 
battery capacity:

AH is a total measure of how much energy the battery contains.
Suppose we had a perfect 10AH battery.  This means that the
battery will be able to supply 1 amp of current for ten hours.
It should also be able to provide 10 amps of current for one hour.
In the real world it doesn't work that way.  If you draw too
much current you use a lot of the energy to things like heat
which causes the battery to lose efficiency.  The less current
you demand, the better the performance.

All of the above really applies to deep cycle and disposable
batteries.  Rechargeable batteries are a little different.
Car batteries are usually rated in CCA, or cold cranking
amps.  The reason why they are not rated in AH is because they
are designed to be drained by 1% to 10% of their total
capacity.  Constantly deep cycling an auto battery will 
cause failure of the thin lead plates.  I'm not a chemist,
but I imagine that the deposition of lead from lead sulfate
is not uniform, eventually eating holes in the thin plates.

Basically AH is a measure of total energy capacity.
CCA is how many amps you can draw before you have used
up 1% to 10% of your batteries' capacity.

Brian Michalk  <http://www.awpi.com/michalk>
Life is what you make of it ... never wish you had done something.
Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
musician, home-brewer, entrepenuer and SINGLE!