On Wed, 31 Dec 2008 09:58:02 +0000, Richard Edwards
wrote:

On Mon, 29 Dec 2008 12:46:01 -0800, John Navas
wrote:

On Mon, 29 Dec 2008 20:38:07 -0000, "ForeverArsenal"
wrote in
:

"ForeverArsenal" wrote in message
usnet...
Hi.
Could anyone advise please

1 led drawing 10mA off a 12volt car battery,how long would
take to use up 1amp of the battery.

Am I right in saying it would take 100hrs,could someone confirm please.

Amp is current, not battery capacity. That's amp hours (current over
time).

Wikipedia:

The battery capacity that battery manufacturers print on a battery is
the product of 20 hours multiplied by the maximum constant current
that a new battery can supply for 20 hours at 68 F° (20 C°), down to
a predetermined terminal voltage per cell. A battery rated at 100 A·h
will deliver 5 A over a 20 hour period at room temperature.

Your LED is drawing 1/100 amp, so it would draw the same power in 100
hours as a 1 amp load would draw in one hour, or 1 amp hours of
capacity.

Just shows that you cannot trust Wickipedia!
That should read ..

The battery capacity that battery manufacturers print on a battery is
the product of "The hour rating" in hours multiplied by the maximum
constant current that a new battery can supply for "The hour rating"
at 68 F° (20 C°), down to a predetermined terminal voltage per cell. A
battery rated at 100 A·h will deliver 100/(The hour rating) over "The
hour rating" period at room temperature.

"The hour rating" may be 20 it may be 5 depending upon the
manufacturer and the area of the world that the battery is sold in.

The Peukert exponent will mean that the 20 hour rating is NOT 4 times
the 5 hour rating.

The answer to the original question is therefore (because of Peukert).

Based on a 20 hour rated battery a drain of 10ma will reduce the
battery capacity by 1 Ampere Hour in a time that is a hell of a lot
greater than 100 hours.
Just for example based upon a 100Ah battery at a 20 hour rate with a
Peukert of 1.3, a drain of .050A will actually look like .010A.
Therefor a drain of .05A will pull 1Ah in 100 hours.

There is the American Electricians Handbook [or something like that]
which has a whole chapter on lead batteries, specifically the 4000 AH
cells used in submarines. Gives capacity at several different rates.

Casady