Cordless Drill Battery Resurrection

Factual Questions
1

I have a set of light duty 18V cordless power tools (RYOBI brand), about 3 or 4 years old. When the original batteries sat unused and uncharged for about a month and a half, both were completely dead and refused a charge. Figuring it was unlikely for both batteries to crap out at the same time, I tried the batteries in my neighbor’s charger, which is the same model, and they refused the charge in that one as well. I started checking online for new batteries or new cells to replace myself.

After seeing a thread on another board where a poster had brought a completely dead drill battery back to life by repeatedly plugging and unplugging the charger itself, I tried it and now the batteries are working fine again. This actually happened to me in a completely unrelated instance with my cell phone battery when it was really dead as well.

So what was wrong? Did the dead battery just have so much internal resistance that the charger thought it was dead? How did plugging and unplugging the charger help?

2

I lot of chargers won’t charge a battery with zero volts on it’s terminals. I usually just zap them with a power supply for a few seconds, which is probably what plugging/unplugging the charger did.

3

Many battery chargers used to have timers in them. I don’t know if they’re used much anymore it’s been years since I’ve taken one apart.

4

I think your battery packs are nickle cadmium and they can develop a memory as it’s called. Fully discharge them from time to time and don’t overcharge them. The memory often can be broken if you work at it.

Battery University

5

That makes sense. I did notice that the red “charging” light would illuminate just briefly when the charger is first plugged in. Maybe it provides a tiny bit of juice that with enough cycles gives the battery enough volts to put it over the edge where the charger will see it as a good battery. Thanks.