"Fixing" dead cordless tool batteries

[Fuddyduddy1952]

I think this was mentioned before but if cordless tool batteries are completely discharged they probably won't charge but don't throw them away yet.
Today I had a Craftsman 20V that wouldn't charge in any charger. Of the four pins power is on the two outermost ones. They measured
0.3 volts, almost zero. To be sure just measure a good battery to be sure and be sure polarity is correct (mark + to remember).
Now connect these pins to a small battery charger, just a minute or so to bring it up to 10 volts or so.
Now when putting in it's charger it charges normally. It saves money.

 

[Midniteoyl]

Works on some batteries, but not on ones that are completely micro controlled, like Makita, though there is a cheap way to get even them up and running most times for cheap

 

[Midniteoyl]

The OBI interface he used..

 

[wilso]

Interesting tip. This actually lines up with what I’ve seen too. A lot of these packs aren’t truly “dead,” they’re just undervoltage-locked so the charger refuses to recognize them. Bringing them up a bit first makes sense.

It reminds me of how some MAGFAST power banks behave when they’re fully drained—once they drop below a certain threshold, they won’t wake up unless they get a small kick of voltage. Same idea here: the cells are still fine, the protection circuitry just needs to see a minimum voltage.

Obviously, people should be careful with polarity and not overdo it, but for batteries that would otherwise be tossed, this is a solid money-saving trick. I’ve revived a couple packs this way that are still going strong months later.

 

[Oaktree]

I've tried that trick a couple times without much luck. Yeah, you can get the charger to recognize the pack and charge it, but in every case there was (at least one) defective cell that wouldn't hold a charge for more than an hour or so making it necessary to go thru this routine every time. YMMV

 

[grsthegreat]

I’ve tried this trick. Sure, they power back up, but they don’t run the tool very long. They lack the stamina. I found a way better trick. I waited until Black Friday and I got 2 Dewalt 4AH PLUS 2 dewalt 2AH batteries in a pack for $99 at Lowe’s.

 

[WinterDeere]

I never knew that cordless tool batteries could "voltage lockout", and I've been guilty of discharging quite a few to almost nothing. It's not good for them, I'm told, but when you're 200 feet from the shop and need to drive "those last five screws...", stuff like this happens.

I wonder if this is ever a problem for new tools sitting on store shelves, if they take a few years to sell? Who hasn't seen an old "new in box" tool sitting on the shelf at a mom and pop hardware store, that appears to have been there 5 years or more?

 

[grsthegreat]

I know the DJI Drone batteries can lock out. I always keep mine current if sitting too long. Had a friend lose 4 because he left them sit too long unused

 

[Midniteoyl]

I never knew that cordless tool batteries could "voltage lockout", and I've been guilty of discharging quite a few to almost nothing. It's not good for them, I'm told, but when you're 200 feet from the shop and need to drive "those last five screws...", stuff like this happens.

I wonder if this is ever a problem for new tools sitting on store shelves, if they take a few years to sell? Who hasn't seen an old "new in box" tool sitting on the shelf at a mom and pop hardware store, that appears to have been there 5 years or more?

Home Depot just sold off a bunch of Ridgid 1.5AH batteries for cheap that supposedly had 2020 and 2021 serials. People bought them then registered them in the Lifetime Service Agreement. Time will tell if it'll be honored.

 

[rontaki]

I had a Ryobi 40V 12Ah battery that sat unused over a winter season. It must have self-discharged to the point that it would no longer charge. I read about resetting Ryobi BMS (battery management system) boards on Youtube videos, took the case off the battery to find that none of the videos covered my particular battery. I tried a few things, and in the process let some magic smoke out of a little part somewhere on the board. Now it was permanently dead. So I harvested the 21700 Li-ion cells, found a few weak ones and mostly good cells. (Be careful, things can get hot quickly!). I charged all the cells in my lithium battery charger, and they all seemed to hold the charge. What to do with these cells so as not to waste their value? I found a cheap power bank on Aliexpress that was just the case and circuitry, no batteries included. I put some of the best 21700 cells in it, now have a power bank that will charge many a phone or run a USB speaker, etc. for a long time, and it didn't cost much, as I already had the 21700s.