Reviving a Dead DeWalt Battery

[Mike Henderson]

I put a cordless tool away and in the process had the trigger slightly pushed. Not enough to cause the motor to run but enough for it to suck power from the battery. When I tried to use the tool later, the battery was dead. So dead that the wall charger would not recognize it as a battery and charge it. The charger just did nothing when I put the battery into it.

So I started thinking - How can I get some charge into that battery? Just enough that the charger can recognize it. This is what I did.

Here's one of my batteries. I cleaned it up before taking the picture - I was amazed how grimy it was.
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If you look at the connections, there is one labeled B+ and another labeled B-.
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I needed something conductive that would fit into those slots. I settled on two of those thin rulers that you often get as gifts with some other purchase.
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They fit into the slots perfectly.
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A problem is that if you put two batteries nose-to-nose you have to cross the electrical connections because B+ (for example) will be on opposite sides. So what I did was turn one of the batteries over so that B+ would be on the same side.
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Leave them connected like that for about a minute and the dead battery will take enough charge that the wall charger will recognize it and charge it.

Mike

[Frank Pratt]

Good tip. Some batteries (Milwaukee for one) will shut themselves down before going completely dead.

[Mike Henderson]

Good tip. Some batteries (Milwaukee for one) will shut themselves down before going completely dead.

I thought the DeWalt would do that, also. When I'm using a tool the tool will shut off before the battery is completely dead.

I left the tool for weeks with the battery in it and the trigger partially engaged. I was surprised that the battery was completely dead. Then I was panicked thinking I'd lose the battery because I couldn't charge it. I didn't know if this would work but I figured I didn't have a lot to lose if it didn't.

Mike

[Andrew Pitonyak]

All I can say is WOW! That was pretty smart.

[Kyle Iwamoto]

Wow interesting.
This does raise the question in my mind. Is it better to use the battery until the tools shuts off and do a full charge, or partially discharge and charge. For the second case, don't let the battery voltage get to the point where it shuts off, always have the battery topped off. I've read tips that say both. It may not matter with the new cells though.
What say the smart folks here?

[Frank Pratt]

I thought the DeWalt would do that, also. When I'm using a tool the tool will shut off before the battery is completely dead.

I left the tool for weeks with the battery in it and the trigger partially engaged. I was surprised that the battery was completely dead. Then I was panicked thinking I'd lose the battery because I couldn't charge it. I didn't know if this would work but I figured I didn't have a lot to lose if it didn't.

Mike

I guess even with the battery "shut down" there was still enough leakage current to drain the battery. This is good stuff to know, both not to let it happen and how to fix it if it does.

That complete discharge may have affected the battery life though. Lithium ion batteries are pretty delicate little snowflakes when operated outside their intended parameters.

[Frank Pratt]

Wow interesting.
This does raise the question in my mind. Is it better to use the battery until the tools shuts off and do a full charge, or partially discharge and charge. For the second case, don't let the battery voltage get to the point where it shuts off, always have the battery topped off. I've read tips that say both. It may not matter with the new cells though.
What say the smart folks here?

I just use my batteries in the way that is most convenient & pay no attention to when I charge them. Some of my M18 batteries are as old as Milwaukee's M18 system is & they are still good.

That said, in theory, when they are going to sit unused, they like to be at about 70 - 80% charge. The hardest part of the charge cycle is the last 10 or 15%, so if you unplugged them early that may give longer life. But to me, life is too short to burden my brain with keeping track of that kind of stuff, so I just use 'em & charge 'em.

I have about dozen M18 tools & probably 18 batteries of various capacity & they all get used a fair bit, so I figure that's a decent data sample.

[John K Jordan]

...Lithium ion batteries are pretty delicate little snowflakes when operated outside their intended parameters.

Also, lithium polymer. The DJI drone I just got uses lithium polymer. They call them "smart" batteries; I don't know how smart but they apparently have a significant amount of electronics inside. At some time after a full charge they self-discharge a little (I think I remember 95%) since long term storage at full charge is said to be harmful. They come in a deactivated state, not drained but just switched off internally - something about safety in shipping.

When I put one in the drone the first time the controller told me it needed to connect to the internet to update the firmware in the battery to match the firmware level in the drone. Zounds. I don't remember carbon D-cell batteries in the '60s needing their firmware updated.


This does raise the question in my mind. Is it better to use the battery until the tools shuts off and do a full charge, or partially discharge and charge. For the second case, don't let the battery voltage get to the point where it shuts off, always have the battery topped off. I've read tips that say both. It may not matter with the new cells though.

Kyle, I think it depends on the battery chemistry. Nickle cadmium is said to need complete discharge. Nickle metal hydride does not. Lithium ion and lithium polymer are said to be damaged by full discharge but the protection circuitry inside the battery is supposed to prevent that so I suspect it doesn't matter if you run tool batteries until the tool shuts off. But the little lithium polymer batteries used in many inexpensive RC quadcopters and helicopters don't have this circuitry so the instructions say to land quickly turn the thing off when you see performance degrading. I have had to "jump start" these little batteries that had discharged enough that the charger decided was too low, just as Mike described with the lithium ion tool battery.

JKJ

[Mike Kees]

Lithium ion can be charged at any time without affecting their life cycle.