Each year I like to test my batteries and replace those that do not
have enough capacity for a typical flight of 3-4-ish hours with all
the electronics running. I run two batteries so that removes a worry
about loosing power during a record flight. But how do you perform a
good real world test?

My test is basically connecting a resistive load to the battery,
measure the battery voltage every 10 minutes or so. Then wait for the
battery voltage to drop to 11.5Vdc (an arbitratry but safe value).
Simple.

I create an Excel spreadsheet that explains all this - the testing
that I perform, the test rig that I used and templates for gathering
the data and then graphing the results. See http://aviation.derosaweb.net/#batterytest.

I’d love to hear any comments that you might have. Enjoy.

John DeRosa
Johnatderosaweb.com