So i know, that technically this is not a repair of battery, cause i am replacing the elements inside. And maybe a million people have done something similar. But as i see it, it is a repair, cause i am not buying a new one, and it is actually cheaper. And also by my own stupidity i ordered too big elements. So some creativity had to be implemented in the repair :)

So i bought this "Brand" name cordless drill about five years ago. As it was around 30 $, i did not expect anything spectacular. And while it worked, it was grate. Sort of. It is not very powerful, but to drive in few screws and drill small holes in to wood or plastic it was sufficient enough.

But after few months of using it, i noticed that battery drains it self very fast. Regardless if you wore using it or not. After full charge it would hold it for few hours. Again it did not matter if you wore using it, or simply just left it untouched. In few hours it would not work. As i was not doing much household works, and had no projects on my hands. After a while i measured voltage, and to my surprise it would show almost 11 V. So batteries wore dead, cause they could not take any load.

So, since i had another one i did not pay much attention to it, and left it for a year or so in the tool box. Had no plans to revive it, maybe just use as a spare part or need a motor someday. Or just connect it to the power supply and use it as cord drill.
But recently i had to drill and screw a lot of screws. Changing the bits, to drills is very time consuming and annoying activity. So i decided to buy replacement battery. For the life of me i could not find the manufacturers battery to buy. And non brand ones wore from 15-40$. And with the cheap ones i was not sure if they would last. So to buy more expensive one, made no sense, since i payed for the whole drill with few attachments (drills, nylon plugs and screws) as i mentioned before, only around 30 $.

I disassembled my battery. And as i was suspecting, there wore only 8 elements connected in series. Simple math, and from 9.6 V battery it was clear, that i need 1.2 V NI-CD elements. So quick search from eBay and for around 10$, or maybe little bit less (price includes shipping) i was waiting for replacement NI-CD's.

Step 1: Tools & Materials

This project is going to be very simple. Sorry for the lack of photos here. All you need is

Tools: Drill

Screwdriver with TX bit

Hacksaw (dremmel with cutting wheel would be better)

Soldering iron

Wire cutters

Materials: Zip ties

Solder

Ni-CD elements

Step 2: Disassemble the Battery

This step is very easy. All you need to do, is to unscrew four bolts shown in the picture.

Than everything breaks down without any tools. Just don't loose any small clips and plastic parts. So quick release function would not be affected.

Step 3: Surgery on the Enclosure

So this step could be avoided all together if i ordered the right dimension elements. In my own stupidity i just payed attention to the voltage, not actual dimensions of elements i ordered. So they wore a little bit too big. And enclosure would not close at all. So i decided to cut off the bottom part.

And after it to reattach it wit glue or zip ties. In the end, i would suggest to get some kind of epoxy resin to fill the void which is going to be left. Cause otherwise dust and dirt will get in. And eventually it may lead to shorting out the battery.

Step 4: Soldering New Elements and Installing Them in the Enclosure

Soldering is very easy. Just 8 elements in series. So take a look at your existing old battery insert, and you will get good idea how to put them in row, and solder the fastest way. Just copy the "design".

And after 5 minutes after attaching the contact plugs from old battery, you will be able to put everything in the enclosure. Before assembly measure that you have around 10 V. If you don't get voltage, that means you missed one or more connections. For example on photo, i am measuring only 7 elements. Check the continuity with multi meter. If you have soldered all elements. See maybe you have some "cold spots".
At this point don't forget to drill some holes in cut of parts for the zip ties. Then insert the elements, and put on part with quick release (include all metal pins and plastic push brackets). Then attach bottom part (which was cut off) with zip ties. If all connections wore soldered correctly, and you did not broke anything else trying to cram everything in their places, you should have working battery.

Step 5: Final Thoughts

So, 30 minutes in your garage and 10 $ later, you have working drill again, and satisfaction of achieving something :D So for now i left my batter Frankenstein like. But along the way, i guess i will have to cover the gap. Also, this technically should also increase the capacity of the battery. Original was 1.25 Ah, if Chinese manufacturers stated real data (which it would not surprise me if they blow up numbers) new ones should have 2.8 Ah. So more than 2 times the capacitance. That means more bzzzz for your buck :) All in all, i am satisfied, that i have another drill on my hands.