DIY: Squeeze Extra Capacity From Old NiCd Batteries





Introduction: DIY: Squeeze Extra Capacity From Old NiCd Batteries

This time I’ll show you how to squeeze some extra capacity from old NiCd batteries.

How I did it - you can check by looking DIY video or you can follow up instructions bellow.

For this project you will need:


NiCd Batteries


Soldering iron

Screw driver


ImaxB6AC V2 or other smart charger

Step 1: Preparation

I got 3 18V batteries from old Ryobi cordless power tools. All I known - that those batteries are faulty or not holding charge. I want to check, does it possible to make 2 reasonably good batteries from 3 faulty.
First is need to take them apart and take a look, how everything looks inside. Sometimes it’s clearly visible bad cells.

Looks like someone already was fixing two battery packs before me. I forgot to show batteries voltages, but I remember that one pack was at 12V and two others at 8V.

Step 2: Charging...

The main tool for this process is Imax B6AC V2 charger.

First I charged all batteries fully up. They all nicely took charge and there was no need to make zapping process.

After full charge, I discharge each pack to 12V. Why 12V? This pack is made from 15 cells connected in series and safe limit to discharge each Ni-Cd cell is to 0,8V. 15 x 0,8 = 12V.
I repeat this process few times to eliminate any possible NiCd memory effect. Used cycle discharge/charge function.

Step 3: Discharging and Looking for Bad Cells

After that I take one by one cell and discharge them at 2A of load to 0,8V cut of voltage. Like I said 0,8V per cell is totally acceptable for NiCd cells. All results wrote on each cell.
And now I can see how good or bad are all three batteries.

Here is connected 15 NiCd cells in series. So battery is good, as good is worst cell connected in series. The idea is to take a look and find worst cells and replace them with betters.

Step 4: Testing Results

Here is some testing results. It’s clearly visible, that first and second batteries are better than third.
It’s definitely need to change 2 cells from first pack and three cells from second. Last battery will be a donor.

After some calculation I decided to replace some more cells in first battery, by using second battery pack best cells. Idea is to make one strong battery where cells capacity will be 1200mah or better.

In same method I’ll upgrade battery number two, that all cells will have 1000mah of capacity or more. Last battery pack will be a donor…

Step 5: Separating Good Cells

It’s time to disassemble battery and separate good from bad cells.
Because I’ll use same cell tabs, I’ll disconnected them very carefully. I used a knife and twisted under a tab. By applying tension, spot welds will pop out. It’s quite ‘tricky, so don’t rush and save your self. And of course - don’t short cells.

Step 6: Soldering...

Arranged cells in final battery shape and started soldering.

Step 7: Final Assembly

Time for re-assemble to battery housing.
If everything was done properly it should gives us around 18V.

Step 8: Conclusion

I checked battery capacity before disassembling and now I could compare it with battery capacity after cells regrouping. There was 1200mAh in beginning and after regrouping cells I got 1400mAh of capacity. It’s about 17% increase. Not bad at all.

So, if you’re working on NiCd batteries powered cordless power tools and have some issues with battery capacity - you could squeeze some extra of capacity like I did. Especially, when this fix cost almost nothing, just your time.



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Thank You. This is a great project if you just casually use your tools. Batteries are way too $$$$.

I have a dozen old Ryobi 18 volt batteries that I was someday going to rebuild.

But I am too busy with my tools and found the new Lithium Ion Batteries are well worth the price especially if you can wait for a holiday sale.

Now they will go to the yearly hazmat collection or back to HD for recycling.

I might even consider rebuilding them using 18650 Lithium Ion Batteries If I knew a way to charge them without causing an explosion. Also finding quality 18650 batteries that do not have fake capacities at a reasonable price would be a challenge.

Get a laptop battery and pull it apart for your 18650 batteries. You can get `new` old stock dead cheap on eBay. I got one with 12 batteries for £6 ($10) and they were Panasonic 2200mAh!! Absloute Bargain!!

Soldering directly on batteries is a bad idea, you have to heat the end of the battery to more than 200 degrees celcius to solder them.

A better idea is to cut the tab in half, bend them a bit away from the battery and solder a bit of wire between the tabs.

That way you have a lot less thermal stress on the batteries which is really bad for them, batteries can explode if you heat them too much.

Better than nothing...

If you solder the wire really quickly, and cool the battery off really quickly, I doubt anything would happen... If one of them catches of fire, make sure to leave a window open! ;)

Wrong chemistry, NiMH and NiCd don't catch fire, instead venting gas and electrolyte, reducing the already low capacity of an old cell.

But they can ignite their packaging materials. Ask me how I know.
I managed to get it outside before black smoke started to pour out of the battery and hot plastic dripped from where the heat from a shorted cell melted through the case.

You also assist yourself to get a better solder joint because you can heat up the thin metal connection to the required temperature more easily. Particularly a good idea if you have a small iron.

Glad you pointed this out SA007. NiCd and NMh cells actually have vents that can be compromised if you are not careful when soldering to them. Safety first!

I have revived bad NiCad cells from the "shorted" malady or ailment by striking (hitting) the electrodes with the contacts of a car battery charger (uses rectified and unfiltered 12 volts) for a few times. Sparks fly because of the internal short, but that fuses open the short and revives the cell.