My backup battery test kit gave me a false reading on a job in Springfield

It happened yesterday when I was finishing up a panel swap. The tester showed a full charge on the new 12V 7Ah battery, but the system threw a low battery fault an hour after I left. I drove back, pulled out my multimeter, and sure enough, it was sitting at 10.2 volts. I swapped in a fresh battery from my truck and the fault cleared right up. Has anyone else had a battery tester just stop being reliable out of the blue?

3 comments

3 Comments

margaretshah7d ago

My old Midtronics unit did that after about three years. The internal calibration drifted and it would show a full charge on batteries that were nearly dead.

hugo_nelson6d ago

Actually, that's the opposite of a calibration drift. If it showed full on a dead battery, the unit was reading voltage way too high. Classic drift makes it read low. Saw it all the time. A high reading like that usually means a failed component, not just calibration. Different kind of failure.

the_karen5d ago

I read a forum post from a guy who fixed a lot of those Midtronics testers. He said a high reading like that is almost always a bad voltage reference chip on the main board, not just the usual sensor drift. The part was a specific 2.5V regulator that would fail and send the wrong signal to the display.