How to convert between Amp-hours and Reserve Capacity -
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Unread 01-02-2013, 11:48 PM   #1
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2004 TJ Wrangler 
Join Date: Dec 2012
Location: Prescott, AZ
Posts: 282
How to convert between Amp-hours and Reserve Capacity

To cut to the chase: All you need to do to convert your battery's reserve capacity to Ah is multiply the reserve capacity by .417.

Here is the background
After I got a new battery for my jeep I was trying to find the Ah rating of the battery - the first site I cam across that had the specs for my battery showed something called "reserve capacity." My battery had a reserve capacity of 105 which seemed very high. I did a little digging and found that reserve capacity is not the same as Ah, but instead is the time in minutes that a battery can last under a 25amp load.

The derivation
To convert between the two units you first need to convert the reserve capacity time into hours by dividing by 60. For my "105" battery my reserve capacity is 1.75hours under a 25amp load. Now all you need to do is multiply the reserve capacity n hours by 25amps to give you the equivalent Amp-hour rating of your battery. This means the Ah rating of my battery is 43.75Ah. As it turns out, because of the order of opporation, it doesn't matter which order you do these two steps in. So, divinding 25amps/60(minutes/hour) gives us a constant around .417.

Hope this helps some people.

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