From the following site: http://www.usbattery.com/faq.htm

Q:What size battery do I need for my application?
A: Determine how many amperes your application needs from the battery and
for how long. Multiply the two to obtain Ampere Hours required. Increase
this by 20% for a safety cushion, and from our capacity charts match a
battery which will deliver this many AH for the required time, and voltage.
Connecting batteries in parallel adds AH, and connecting in series adds the
voltage. In either case the energy (WH) storage capability is increased by
the amount of energy each additional battery provides.

Marcelo Y.

> I'll help with the AHr question, but I'll let others
> establish why you need to re-think this problem.
>
> AHr is simply Amps (current) divided by time (one hour).
> This describes the capacity of the battery. For instance, a
> 10 AHr battery should be able to 10 amps of current to a
> load for 1 hour. You should be able to get larger currents
> for shorter periods of time.
>
> However....
>
> As the current from the battery increases, the battery
> voltage goes down, potentially down to zero. This makes it
> difficult to run DC-AC inverters, etc., from a small
> battery, and can cause damage. A larger battery can hold the
> voltage up for a longer period of time.
>
>
> John Pearson wrote:
> >
> > I want to run a 850 watt AC motor for 10 seconds off 12 volt batteries.
> >
> > How many 12 volt batteries and what AH would they need to be. I
calculate 6.5 batteries (80 volts)?, but the AH part has me puzzeled.
> >
> > Thanks for any help
> >
> > John
> >
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