"Jumping" a battery

[slownsteady]

Recently I was talking to a Milwaukee rep. at the local big box store. We were talking about how a power tool battery sometimes goes bad and you are unable to charge it. He said that it's due to the battery running so far down that the charger can't [detect] it. He said he's heard that there's a way to give the battery a jolt by jumping it from a good battery, but he didn't know exactly how it's done. Anybody hear of this? Or have tried it?

 

[bud16415]

I don’t know for sure but I bought a new charger to keep on my tractor over the winter. All my old chargers just pump out juice and are not at all “smart”. This new does more than just charge the battery and has some smart features that help actually maintain the battery. I remember reading it won’t be able to charge a severely discharged battery in normal mode. I has a work around where they tell you if you want to try and bring a totally discharged battery back you press one button and hold it for 5 seconds and it then goes into a brute power mode and just pumps out juice like an old charger.



I think power tools have a great deal of smart function because they are normally used indoors and they don’t want to take any chances. Also they are not old lead acid batteries that can take a lot of abuse like a car battery.



It could be a little risky to just jump a good tool battery to a dead one direct. Depending on the resistance of the dead one you could get a lot of current/heat quickly it might fix the bad one or fry both. One way around that might be a resistor in line with the jumper to limit the current and try and bump it enough that a regular charger could take over.



This is just a guess maybe someone might know more.

 

[Snoonyb]

This is the method I've used for several decades;

There are differences in RYOBI, DEWALT, BOSCH, MILWAUKEE, RIDGID & SKILL which you'll discover, when attaching between the two.

 

[PJB12]

On NiCd & NiMH, you can tap with a small 9 volt battery. It clears the dendrite crystals that build up.

With safety eye wear on, tap positive to positive and negative to negative:
VERY BRIEFLY (as fast as your hands will move) tap several times, then charge like normal. If you have a meter, tap until the battery shows at least 25% of the rated voltage. Sometimes this will be a long lasting fix, sometimes short term.

DON'T do this with lithium batteries. They can explode, or at least be damaged. (Nearly all lithium tool batteries have circuitry inside the case for sensing and protecting. It'll get wrecked.)

Paul

PS: Rebuilding tool battery packs is rather simple, especially if you purchase cells with the solder tabs already installed. (eBay, Temu, BangGood, etc are inexpensive sources.)

 

[slownsteady]

Video was very helpful. Thanks.
But really, no Lithium batteries??? Aren't they all lithium nowadays?

 

[PJB12]

Video was very helpful. Thanks.
But really, no Lithium batteries??? Aren't they all lithium nowadays?

One would think so.
I just bought an inspection camera with NiMh batteries. I have a 2 year old Porter Cable drill with NiCD. My neighbor's brand news lawn mower has lead acid.