On 6/20/06, Loren Busch <starwagen@gmail.com> wrote:
>
> The answer to another question here on the list raised this
> question.  Given
> that we have the amp hour rating for a battery and also given that we
> don't
> want to draw it down below about 10.5 volts, about 80%.  Does that amp
> hour
> rating assume draw down to the 80% level, or draw down to 'dead', zero?
> I've always assumed that if I have a 50 amp hour battery that I can draw 1
> amp for 50 hours before reaching the point that will require charging, or
> will I only get 20% of that, 1 amp for 10 hours, before reaching the point
> where I need to recharge?
>

It seems the unfortunate truth about Amp-Hour ratings on lead-acid batteries
is that they usually give you the "full drain" rating, and give it to you at
a "slow draw" rate to boot. According to the battery guy I got my Trojan
from, 80% is considered the max discharge without significantly compromising
the battery, just as Dennis says. He added that even 80% is pretty hard on
the battery and that if you want it to REALLY last you should stop before
50%. Basically the guy's recommendation was to get the largest battery I
could afford (in terms of both cost and weight/size) and then use it as
little as possible!
One thing that sold me on the Trojan was that their specs never claim any
specific AH rating, but rather give several different "capacity
calculations", e.g. capacity minutes at 25A, 56A, and 75A, plus 5 hour and
20 hour rate AH capacities.

--
John Bange
'90 Vanagon - "Geldsauger"