DeWalt 40V batteries is not being recognized by the charger and refuse to charge correctly. The charger flashes red which means something is wrong.
What happens here is the low-volt cells take a bit of kick-start to get moving again. It’s an easy fix for dead cell in the pack. There is no reason to throw away a good pack when you know how to do this.
The easiest thing you can do is grab another DeWALT battery of same voltage. It doesn’t need to be a brand new one but at least one that has a little juice in it. You want to shared the load across both batteries and this quick jump starts up dead cells within.
Knowing how to identify the terminals is the obvious next part. Positive to positive? Right. Negative to negative? Yep. And if not, it will bite you in the butt right now. Set both batteries down together on your working area and look down at the rails on each one. It’s easy to tell which is which then.
So you take care to connect the wires between the two packs making sure positive wire connects to the positive terminal on the other unit. Same for the negative. It’s snug and it seems like they are connected well. What this does is bridge the gap in power and let it flow back into weak pack.
You hold that in place for maybe 15 seconds and then release the connection. It’s not a long time but I’m guessing that’s enough to trigger whatever the juice is that does something. There were no warnings to let go right away at the first sight of smoke. There was just a gentle electrical handshake between two pack, with no smoke and no nothing.
DeWALT happens to make a pretty sweet pack which is what I had handy in these demos. Honestly, other brands are pretty good too sometimes when all you have is some spares of something else kicking around. There’s enough voltage compatibility here for this trick with a Greenworks 40V in another demo. That’s the point, it’s the principle and not the name on the package.
As far as setting up the cross-brand connection, its all the same process so once more, a negative goes to a negative and a positive goes to a positive. Good contact is key with transferring current, so you want to be sure to strip off the end of the wire correctly. In this case, we had the black DeWALT pack sitting patiently next to green battery.
Fifteen seconds, that’s what we’re aiming for with the link again, and you pay close attention to make sure it all goes off without a hitch. There were no foul odors and no melted wiring in testing, which is a quick fix but one that works. This process gets enough juice into the dead battery to get it reading as intended.
Using a DC Power Supply
The third option is a bit more advanced then swapping batteries, but it is also a bit technical. If you don’t have any spare batteries on hand whatsoever, a DC power supply will do the trick when you need that kick in the pants to get her fired up. With a bench unit, you know exactly what amperage and what voltage it put out so you hook it up carefully and go to town.
Setting the voltage range of thirty to forty volts is important. And for the current limit you want it to be about one amp. Too much current will burns the cells in your pack. When working with this kind of equipment precision beats brute force. You work those dials on the power supply carefully.
Plug the leads from the supply into battery terminals. Negative to negative; no hesitation. Positive to positive. At the display, the numbers begin to climb toward the level you want. It’s a clean looking, professional set up on your desk.
As with all these other batteries, you hold it there for a full 15 seconds and voila. You’re done. Quick removal of your leads is key to keeping consistency here and being sure you get results every time. In this case, the short burst of juice worked perfectaly.
If it worked, the indicator light will change from flashing rapidly to blinking slowly once you put the restored pack on the charger. If it’s still slow red, that indicates it’s charging just dandy now and there are no issues with the battery taking a charge. After one last check like that, your tool should of been good as new in no time.
