I have several UPS (uninterruptable power supply) units to keep important electronics running through short power outages. Designed for SLA (sealed lead-acid) batteries in a commodity 12V (volt) 7AH (amp-hour) form factor, I retrofitted one of my UPS with LFP (lithium iron phosphate) battery packs designed to the same form factor for use as a drop-in retrofit. I performed the first runtime test immediate after they were installed, intending to repeat the test at regular intervals. I had thought repeating the test every 6 months would be informative, but I recently realized it's been 9 months. Oops. Well, it should still be informative. All the same equipment are still plugged in to this UPS, so the test was a matter of setting aside a period of time when I can be interrupted every 5 minutes to write down the estimated runtime remaining displayed on the UPS. Then those numbers were plotted on the same Excel spreadsheet to generate this chart:

The new line (in orange) is slightly lower than the line from the first test, but behaved mostly the same indicating minimal degradation after 9 months. It shares the odd initial jump to 295 minutes estimated runtime as soon as I unplugged it, and two large drops I can't explain. By the 75 minute mark estimates from this second test were 5-10 minutes lower than the first test until 165 minutes when the two matched up. I wouldn't put too much weight on that, though, as the first test established that runtime estimate became unreliable around this point due to different discharge curves between SLA and LFP battery chemistries.

I stopped this test after 210 minutes, or three and a half hours. Given the unreliable time estimate beyond 180 minutes, I expected no useful data from draining this UPS further. I was satisfied my UPS can still keep my components running for at least that long, which I felt was the most important part.

I didn't intend for a 9 month test interval, but now that the precedence has been set, I've set a calendar reminder for myself to repeat this test at the 18-month mark: Test #3 is scheduled for April 2025.