Repacking 7.2V NiCD Drill Battery With Lithium 18650

I have had this drill driver for many years. Originally I bought it used because it had a key based chuck, which was required to use the Skil Bit Click as seen in the photo.

In 2013 I bought a knock-off ni-cad battery for it, and recently that's been getting super-hot while charging so I was worried about damage.

What can I do to get more life out of my old tool ?

Yes I know replacement is a thing, and I've had to buy into 36V ecosystem with a new mower and hedge trimmer, but these don't fit any hand drills. Plus not throwing away things is good. Finally I love the bitclick and no modern hand drill uses a keyed chuck, so that would also have to move over to a new drill driver body.

This other drill/light turned up for $5 at a local swap meet. Brand new and unused, the seller said it was a prize that had sat in a garage for a decade. Of course the battery should be dead after all that time with no usage.

However I got it home, the battery took a charge in my charger, but the new charger was dead out of the box. This might have been why it was put ROPAed initially. The chuck is brand new, and the new drill has a 2 speed gearbox and torque settings.

Upshot, I now have a spare battery so if I screw this up, there's a fallback. (slight fudge, these photos were after this was all done, so the Ryobi brand battery came in this set, and the knockoff should have been in the first photo.)

Now its time to figure out what we have, and therefore what we don't have.

I started by popping the bottom cap off the dead battery. As you can see the contents are fairly minimal, with 6x 1.2V Nickel Cadmium batteries in series, and two thermistors or heat sensors.

> To clarify, I am busting open the knockoff battery pack, not the Ryobi branded original pack. There will doubtless be variations between the original and aftermarket pack. The battery manufacturer will certainly be different.

Result: I need 7.2 Volts and some way to secure replacement batteries inside these dimensions.

At one point I thought of an external battery, but now I realise two 18650 cells at 3.6V each in series would provide the required voltage.

I wondered about C and discharge rate, so ended up buying four batteries and two holders with a mind to making an extended length battery if required.

I bought two battery holders designed for PCB mount, and four 18650 cells. Due to airline restrictions, I can't order batteries from the usual discount asian suppliers so had to buy them locally.

The holders are simple and cheap, and are not internally connected allowing for serial or parallel use depending on how you wire them.

I did have to snip and file a little plastic off the corners of the battery holder, but it wasn't structural. The edge was left relatively jagged so later the hot-glue would have something to hold onto.

My idea is to remove the two batteries and charge them externally. I ended up with a spare pair so these can turn-about and let me keep drilling while the first pair charge up.

So we need an access panel. I drilled four holes in the corners as a target and stress-reliever. YES I used the drill and the original/backup battery pack for this. I ended up drilling off the old label, cos why not? The hole is taller than the 18650 and can clearly see the metal battery clamps, but the top/bottom walls of the holder are just under the case. I had an idea to use something to cover the gap, but this was not necessary in the end.

Then I used a thin dremel-style cutoff wheel to buzz through the plastic between the holes. Being some kind of thermoplastic it got soft and formed some slag on the edges, so that needed trimming with a sharp knife. The slag also tried to coat the cutoff wheel, but it was almost worn out anyway.

To make the battery holder a 7.2V device, I had to bridge the Positive on one end to the Negative on the other. I recycled one strap of battery joiner from the old chain of NiCD, on the basis that thicker would allow for higher current. I used normal lead-free solder and had to flux the strap so the solder would stick quicker and the heat didn't have time to deform the plastic.

This battery holder has + and - embossed into both ends, which is confusing, so I ended up printing a new bright-yellow label.

The wire was simply recycled from my box of donor wire. Nothing special there. None of the connections can short, so I didn't bother with heat shrink. Instead the hot-snot will do that.

Lastly, to get the metal tabs to sit right I used some small pieces of double-sided foam-backed tape to support them.

The red ribbon is a short length of Bias binding, which will be used to pop the batteries loose from the holder without levering them loose. This causes damage over time and while that may be okay on disposables, I don't want that on rechargeables.

Reassembling was straight forward. I used hot glue to hold the ribbon on the back of the battery in a convenient place, then once that was set I simply slid the battery terminals up from the bottom and seated it with my fingers through the access hole, then the battery holder came after it. This is why I used a little more wire than strictly required.

While there was still access, I used liberal doses of Hot Glue under the top battery terminals to provide some support. The old battery held the terminals up in place by being the right length, but mine has some empty space above and below the holder. So hot-snot will hold these in place.

The two temperature sensors are sitting below the battery pack out of the way. As such they will never get as hot and fulfill their function, but I won't be charging this in place so its irrelevant. However removing them would probably upset the drill.

Side note - there are two sensor thermistors because this battery pack fits both Ryobi and AEG tools. My original stock battery only has one sensor pad.

Then I added more hot snot glue in any cavity that might need it. Up the sides of the battery holder, and across its tail. Lastly I snotted under the tail cap and clicked that into place.

It works - perfectly. The battery fits both drills and the torch(flashlight) like it was designed to.

The voltage out the top is about 7.5V and I haven't charged these 18650 for a while. So any comparison of torque or runtime is premature.

However we can compare the weight. The original battery weighs 342 grams, and the new one weighs 144 grams for a saving of 198 grams, or 58% removed.

That's the same as going from 12 637/10000 Ounces to 5 1589/20000 Ounces

In terms of rated energy density, we've gone from 2.0 AH to 9.0 AH so runtime should increase by 450%. This remains to be tested.

Torque - I wish I could measure torque. If the new battery is lacking in torque its because the current is insufficient, and I would have to review this with either 4x 18650 in a 2+2 configuration, or possibly explore multiple 16340 to stay inside the dimensions required.

Any questions, please ask.