Easy 'repair' for rechargeable batteries

For those of you like me with a shelf full of 'dead' battery packs for drills etcetera, here is an easy fix. I had an old Bosch 14.4V drill, the battery would not hold any charge, put it in the charger and within 2 minutes, the green flashing LED (meaning charging) would turn solid (meaning fully charged).

[ame="http://www.youtube.com/watch?v=A5k0ljHLF58"]Revive Your Old NiCd Batteries...! - YouTube[/ame]

Saw the above on YTube, tried it,.... it worked, :stunned: so a batt that would not hold any charge is now taking 1 to 2 hours to charge and working well!

I put the battery in the charger and switched the supply to the charger on and off 10 to 20 times and then left it to charge, then when the LED went solid, did it again and again, each time there a longer period between having to do this,.... now it fully charges.

Saved me £20/30.



Last edited:

Randy V

Lifetime Supporter
I've boosted batteries by hookng them up to a fully charged car battery that will essentially force charge the dead battery a little and then stuck them in the charger for a full charge. It doesn't work all the time though.
Another trick was to reverse polarity charge the battery for just 1 second which supposedly burns off some salts or something like that. I have not done that one as I'd rather pay for another battery than risk a fire or explosion.
So what is happening with the repeated off/on cycles of the charger?
Maybe it does a momentary charge (like the boost I was talking about) or somehow does a forced reset of the charger "brains" or ??????

I have a couple of totally flat 24 Volt Bosche units I will try this on.. I gave away my Ryobi stuff because like the guy in the video, his Ryobi's were toast...
Hi Randy

the chargers have charge management electronics within, to allow the charger to know when to stop charging the batts, basically the charger can do this in several ways:-

monitor the current being drawn into the battery under charge
monitor the voltage of the batts.
temp measurement is also involved in more sophisticated management solutions.

I believe what is happening here is that the bad battery is not drawing current (like when fully charged), so the charger is switching off the charge current prematurely. Switching on and off does something to the battery possibly momentarily giving it an over-voltage to allow a proper charging current to flow (like it used to), thus the charger management circuit detects the correct current being drawn and continues to charge as it used to.

Your jump starting solution is similar, in that you are forcing the current in and 'resetting' the chemistry to some extent.

WHo knows!

There is a pretty well known failure mechanism for nickle cadmium (NiCad) batteries where metalic "hairs" grow within the cells creating shorts or partial shorts within individual cells. When this happens the charger will not see the expected voltage rise over time with a specific current input to the battery and will therefore shut down.

One of the "tricks" to restoring older NiCad cells is to charge a large value capacitor (5,000 to 10,000 uF with appropriate voltage ratiing) to a voltage of 2 to 4 times the cell or battery pack rating and then connect it to the battery (+ to + and - to -). The capacitor will discharge a large but short duration current through the battery and potentially vaporize the offending "hair". I believe you can find more information by searching the web using terms like "restoring NiCad" or "recovering rechargable batteries" etc. Note that this is only valid for NiCad battery chemistry and has some potential dangers associated with it. This should not be attempted for nickle metal hydride batteries or lithium batteries.

It may be that the repeated charging start cycles push enough current through the "hair" enough times to eventually melt it or vaporize it. Most charges start their cycle with a fixed current to get voltage feedback from the battery and asses its current status.

I have done the capacitor trick to several batteries with good success, at least short term. It does seem that once a cell goes bad it is never quite as good as a new battery. Also, there is a possibility of short term and long term damage to the battery, and you... If you attempt this safety glasses and a face shield would be in order (maybe gloves and a long sleeve shirt also).
Yes, should have specified NiCd only on this 'trick', also placing the battery in and out may not work, you need to switch the charger on/off repeatedly to give it the thump it needs.
Hi All,

I've used a starter/charger, designed for starting cars with flat batterys, to save ni-cad drill batterys. Connect up the starter/charger to the drill battery, set it as you would to start a flat car and give it a few second burst at about 50 amps. Try it back in the drill charger, and if it still does not work, blast it again on the starter charger for a few seconds(be carefull of the battery pack getting too warm).

Ive done this on some Bosch 24v batterys that had been left flat for years because they were dud. Might not have been as good as a new battery, but they worked well enough