Chosen Solution
I have 2 Black & Decker 20 volt “Matrix” batteries. During another household project, I used the battery as a power supply for something else. Low draw, was not getting hot. Discharged down to 17 volts. Now when I plug it in, charger just shows “bad battery”. Another just shows “bad battery” on the charger when I plug it in. It’s practically new but I have no insight on that one. Anyone familiar with how these opperate that might have a fix at least for the first one? My suspision is that somehow the battery knows it was used for something it should not have been. If that’s the case…can it be reset? Same problem with older 18 volt “Firestorm” battery. This could be age…but every battery (3) shows bad?
Hi Jason. Sometimes you can revive a “bad battery” by manually charging the battery with a variable voltage power supply. In this case you have a 18.5v battery which is operating at 17v. You know that the battery pack is composed of at least (5) 18650 lithium ion cells in series. Voltage adds in series. 18650 cells have a nominal voltage of 3.7v (3.75 = 18.5v). Most 18650 cells have a charging voltage of 4.2v. If you charge the pack at 21v (4.25=21) or just slightly higher (~21.5v), you should be able to boost the nominal voltage of the pack closer to the desired 18.5v. I have found that manually charging a “bad battery” with a variable power supply for 10-15min will bring up the pack to a level where the genuine drill power supplies will be able to recognize and charge the battery pack again. Good luck.
I have no experience with Black and Decker batteries, but have had DeWalt batteries do that. I would take the bad battery and place a penny in each of the power terminals. See pics. Take the good battery and make SURE to connect (+) to (+) and (-) to (-). Connect only for several seconds. Place bad battery on the charger immediately. I have revived several batteries in this manner. Please use caution when using this procedure. As a precaution make sure to do this outside in case of fire.
