Thanks bluesubaru

First you need to install the battery-status application

here's the download link
http://nitapps.com/dists/chinook/use....0-2.armel.deb

After this is installed you can open up the terminal application and type

battery-status -d 30

and then press the enter key.

This will create an entry in the terminal screen with the time and percentage left every half hour, I let mine run for two hours, to make sure it was consistent.

First I did this with no cards in either the internal or external SD slots, and I also was not using Virtual Memory either. This was to establish a baseline. Then I ran the test with each of my different cards in the external slot. I also did a test with each in the internal, but you probably don't need to do the internal slot test, I was just seeing if there was any difference, and there wasn't.