I have a Testo 875-1i Thermal Imaging camera that, as a daft expensive toy, had been sitting unused for a while. When I needed it, I noticed that the battery (marked 0515 1100) was no longer working at all. It would not power the camera, and the camera wouldn’t charge it.
The camera has had little use compared to the levels it was designed for, so the battery was not degraded due to discharge cycles. I suspected that the charge controller was refusing to charge it because the cell voltage had fallen too low.
The cells themselves were registering just over 1.55V each, so they were pretty much fully drained. The lower threshold for a deep-discharged cell is typically 1.5V, below which the cell should be discarded, so I figured if I could push a surface charge into the cells, then I could persuade the charging circuit to activate.
And it worked! So I don’t have to throw out a serviceable battery, or fork out £130 or so for a new one.
Warning: This article is not a recommendation that you should do this yourself. Lithium Ion batteries can be dangerous. They hold a lot of charge, and can deliver a lot of energy in a short amount of time. If you suspect the battery is actually faulty or has been depleted through use, then just replace it. Certainly do not try to revive a cell that has fallen below 1.5V, because conductive bridges may have formed internally. In my case, the cells were very likely still above the safe pre-charge level, and I took the precautions of checking for signs of overheating repeatedly during charging. If you are not confident you know what you are doing, play safe and buy a new battery.Continue reading