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

Picture of 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...

Picture of 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

Picture of 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

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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

Picture of 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...

Picture of Soldering...

Arranged cells in final battery shape and started soldering.

Step 7: Final Assembly

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

Step 8: Conclusion

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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.


norbertomoritz (author)2016-11-14

Simple but clever, thanks.

FlyinngDolphin (author)2016-10-27

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.

TonyC41 (author)FlyinngDolphin2016-11-11

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!!

SA007 (author)2016-10-27

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.

Yonatan24 (author)SA0072016-10-27

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! ;)

ac-dc (author)Yonatan242016-10-27

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

harvsch (author)ac-dc2016-10-30

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.

TCSC47 (author)SA0072016-10-28

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.

leon.t.gibson (author)SA0072016-10-27

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!

RaymondR6 (author)2016-10-27

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.

JPcreo (author)RaymondR62016-10-29

Hi thanks for the tip. I'm not clear on the connection. You quickly touch the battery positive with the charger positive? and so on with the negative to negative? Thanks again for your time.

Nwerd714 (author)RaymondR62016-10-28

bon jour,

I'm not sure if this applies to these types of batteries as well, but for lead acid batteries, I've seen a video that explains how some batteries build up small sulphate crystals, but long gaps between charges make the amorphous lead crystal become a stable crystalline deposit from negative side to the positive (reducing active material) and that's why they lose performance. However, by "zapping" the terminals with a short burst of high current (like a car battery charger), it breaks the crystal and is allowed to be reused until it builds up again from one side to another (which is what I do too & is kinda bad, mm k). I've heard to overcharge it at about 200mA-ish per cell (15v or 16v on a 12v) for up to a day and get the battery warm to help dissolve crystals again works better. Haven't tried it, but there's a scientist somewhere who has & id believe him before myself

jimvandamme (author)RaymondR62016-10-27

I've zapped many a NiCd this way and got most of them to work. For a while.

rcada (author)2016-10-29

I have found Black&Decker & Ryobi batteries were the worst to hold charges. I just scraped them and invested in lithium ion cells and Makita equipment. No problems how and they work every time I go to use them and I do use them a lot

Good work to make one good battery out of three.

e5frog (author)2016-10-28

Seems nice, might be cheaper to buy new cells than to get one of those chargers though.

TCSC47 (author)e5frog2016-10-28

You will find that the B6AC battery charger is extremely useful and versatile. Mine cost only £20 from China. It might be a copy but it works fine. Difficult to understand how to use it though because the instructions are in Chinglish.

e5frog (author)TCSC472016-10-28

Wonderful Chinglish, if you feel down, grab one of those manuals and have a good laugh. ;-)
It's a nice instructable, very useful if you have more time than money on your hands. I was worried about the heat problem but I see it was addressed already in the comments with a good tip how to better mount those batteries together again.
I put a PSU and a cord on mine, rarely use the tool so the batteries are always either discharged or need to be in the charger. If sizes match you can put the PSU inside the battery compartment.

TCSC47 (author)2016-10-28

Good one.

SiemensWindPower (author)2016-10-27

Done the same work a lot of times during the last couple of years.

I discovered that mostly it's just a single cell which collapsed.

Just by-pass the faulty cell with a heavy insulated wire. The battery pack then drops from 18 volt to 16.8 volt which is ok for the most machines for common diy work

LloydEwing (author)2016-10-27

My experience from trying to make solder connections on ni-cad AA
batteries is that after soldering the batteries will only last a short
time. They seem to be OK for a little while, but even it you are trying
to rebuild a battery pack with new cells soldering damages them so
badly that they don't last. I like the suggestion from przemek if you
are trying to reuse old cells. Otherwise you need a small spot welder
like one from the Instructables I have seen in the past.

przemek (author)2016-10-27

When you cut up the chain, just cut the metal tabs half way between the
batteries, leaving stub tabs attached to the batteries. This way, when
you reassemble the cells you can solder the tabs (perhaps using a
bridging piece of wire across both tabs). It'll be much easier to solder
because you will be heating just the tab rather than the entire
battery, which by the way tends to damage it.

sconnors (author)2016-10-27

I have had good luck just recharging the individual cells in the battery. They seem to get out of balance with use.

draven101 (author)2016-10-27

Great Post. I have to try this out. The one question I have is, how do you know what each battery is capable of if all the batteries are still connected to each other? Wouldn't the connection make the batteries act as a whole battery? And if it was a mistype in the steps in the process, then how do you discharge at 12v? I would like to try but admit I am confused. Thank you in advance for clarifying this for me.

skylane (author)draven1012016-10-27

They pretty much have to be disassembled, tested, charged and retested individually... then reassembeled.

RaymondR6 (author)draven1012016-10-27

Each unit is a "cell" ,and the "battery" is the whole group (I wonder what fool started the single "battey" mistake years ago). Each cell can be measured individually between its two electrodes without disconnecting it. That is how the author finds which cell has to be removed and substituted with a better cell from a donor battery.

ac-dc (author)2016-10-27

This is usually only a short term fix because by the time some cells have died, the remainder aren't long for this world either. I'm suggesting that unless you live in a remote area or in an emergency where it is impossible to get new battery packs, you're better off buying new and recycling those. Better still to get the newer Ryobi Li-Ion packs and charger as they are backwards compatible with their older 18V One+ tools.

ereus (author)2016-10-27

I 've got similar battery an I've remove all and put AA recargable batteries in tree packs of four batteries (it's like in toys). I can extract all AA batteries when I don't use the device and i chage them in a normal battery charger.

ac-dc (author)ereus2016-10-27

That may work but it's quite a pain in the a55 way to use a power tool. Given the high self-discharge properties of typical NiMH and NiCd, even with good cells, let alone old ones, and that these particular batteries are Ryobi which means newer Li-Ion chemistry batteries are compatible with the old tools, it would be better to just buy a new Ryobi set that comes with Li-Ion cells and Li-Ion charger then use the new battery packs with the old tools too.

Today Ryobi has 5Ah or their more common 4Ah 18V packs which will provide a lot more power than your 3 x 4 (14.4V nominal) packs, while providing up to double the Ah capacity as well, plus with negligible self discharge rate, you can grab a pack and go, not have to charge it nearly as often.

HUNDFITZ (author)2016-10-27

The basic problem is that no Ni-Cad battery has ever been used according to the nature of the battery's charge/dis-charge cycle requirement for maximum life. If so, your power drill or appliance should automatically shut off when the cells reach .8 volts. I used to use "C" size ni-cads in an old Honeywell electronic flash unit when I used to do wedding photography. When the cells started to age, before charging normally, I would reverse charge them with my 12 volt car battery charger, I used to get the cells to work for the short periods of use that I needed and suprisingly it was a reliable scheme although not good for extending the life of the cells much farther.

Of course ni-cad cell disposal is a serious problem. I am predicting that dangerous levels of nickel and cadmium salts will eventually leak into water supplies having leached out of old failed dump sites. Make sure you dispose of cells in a manner set forth in your community for safe disposal of old ni-cad cells.


russ_hensel (author)2016-10-24

Just a note to let you know I have added this to the collection: Cordless-Drill-Battery-Maintenance ! >>

Take a look at a bunch of different/similar approaches to this project.

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