Calculating Battery Capacity

Posted by: Steve Laser on Nov 30 2006

While testing the Boxwave Battery Adapter I noticed that my Mugen 1800mAh battery wasn’t performing up to par anymore, but I couldn’t figure out exactly what capacity was left. The battery is only 9 months old, and I was really curious as to how much of its power it retains. So I did some research.

I started off with this article by Menneisyys that discusses tips on extending battery life. He points out the use of AbcPowerMeter, a utility to measure battery load. Next, user YawGlenn in this post, describes the method used to determine battery capacity. Armed with that information I am determined to do some math!

Look out because I have a calculator and just enough knowlege to make me dangerous! It took me a lot longer to understand this than most of the techies/engineers on this site because I’m not built that way. So I’ll make this easy for the simple-minded folks like me. To calculate battery capacity, simply download AbcPowerMeter (I put it into my SD card), and charge your battery to full.

-Next, remove your pda from its power source and click on the AbcPowerMeter icon to start it.

-Click the Start Flag and open a program like GSPlayer or TCPMP and play a movie or music endlessly (I like to do this test with a movie).

-Keep an eye on your pda and wait until the power goes down to about 25-30%, then stop the movie or music.

-Write down what percent of battery power you have left.

-Go to AbcPowerMeter and check out your results

A thick red line represents the average. The thin line is the actual usage. My battery used a total of 769mAh, or milliamperes of power over less than 3 hours. It averaged 381mA at a given time.

Here’s how you calculate your Battery Capacity:

Total power used x (1 /(1 - Battery % left)) = Battery Capacity

769mAh x (1/(1 - 26) = 1039mAh

My Mugen 1800mAh Battery that is 9 months old now has almost half the original capacity. Ouch. Anyway, that’s how you do it.

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