# Calculating amp-hours?



## PACrofter (Oct 11, 2002)

Sounds like a simple question, and it is - if you have all the information you need. But how would you determine the AH capacity of a battery if the amp-hours is not stated? 

I was looking at deep-cycle batteries in Auto Advantage the other day and none of them showed the AH capacities of the different batteries. They showed the voltage, and the cranking amps, and stuff like that, but not the AH capacity.

I'm looking for something in the 80+ AH range for a battery-powered fence charger. Any thoughts on how to do this? The guy who worked there couldn't help me.

Thanks in advance!


----------



## Bearfootfarm (Jul 13, 2006)

3


> ) RESERVE CAPACITY
> What does the *Reserve Capacity *rating mean and how does it apply to deep cycle batteries?
> 
> ANSWER:
> Reserve capacity is the number of minutes a battery can maintain a useful voltage under a 25 ampere discharge. The higher the minute rating, the greater the battery's ability to run lights, pumps, inverters, and electronics for a longer period before recharging is necessary. The 25 Amp. Reserve Capacity Rating is* more realistic than Amp-Hour *or CCA as a measurement of capacity for deep cycle service. Batteries promoted on their high Cold Cranking Ratings are easy and inexpensive to build. The market is flooded with them, however their Reserve Capacity, Cycle Life (the number of discharges and charges the battery can deliver) and Service life are poor. Reserve Capacity is difficult and costly to engineer into a battery and requires higher quality cell materials.


http://www.dcbattery.com/faq.html#3

The Formula:



> *Amp/Hours = (Reserve Capacity / 2) plus 16 *


http://www.chem.hawaii.edu/uham/bat.html


----------



## PACrofter (Oct 11, 2002)

Bearfootfarm, this is very helpful. Thanks so much!


----------



## WisJim (Jan 14, 2004)

If the battery label shows cranking amps, it isn't a deep cycle battery, as a deep cycle battery isn't suitable for the high amp discharge of starting an engine (which is what cranking amps is all about).


----------



## Bearfootfarm (Jul 13, 2006)

> If the battery label shows cranking amps, it isn't a deep cycle battery


Lots of deep cycle batteries are used as starting batteries on watercraft, so they DO list the cranking amp ratings:



> Duralast marine and RV batteries are designed to get you and keep you on the water! Duralast marine batteries are manufactured with the cold cranking amps, reserve capacity and vibration resistance to keep you operating in the demanding marine and RV environments.


http://www.autozone.com/autozone/ac...y/_/N-4b0oZ1z141xg?itemIdentifier=298374_0_0_


----------



## PACrofter (Oct 11, 2002)

Here's one that I think fits the bill:

http://www.napaonline.com/Search/Detail.aspx?R=NBP8301_0056217521

It should provide 116 AH capacity, more than required, and is in stock at the local NAPA store. Anybody have any experience, good or bad, with this brand?

And are there any thoughts on a charger? I have an old one but it tends to overcharge batteries, so I might as well get something that's not going to fry this battery...


----------

