Introduction: Convert 7.2V Cordless Drills to Lithium-Ion Power

So...lets say you happen to get you hands on a beautiful old-school BOSCH PBM V-1 cordless drill.

But it came with a couple of drawbacks:
A) The Ni-Cd battery pack is useless (makes sense after all those years).
B) It didn't come with a charger.

So you come to the logical conclusion. The cost of a new battery pack is more that you ar willing to pay,
and its impractical to rebuild the pack with new No-Cd cells as you don't have a charger to begin with!

So what do you do???

Convert to Lithium Power of course! :-)


All you'll need is the following:

1) 2 x 18650 li-ion UNPROTECTED batteries (branded and new is better) (UPGRADED, see last step)
2) One holder for 2 18650 batteries (cheep on eBay or locally) ---SEE LAST STEP FOR AN UPGRADE---
3) A small rotary tool (I used a Dremel with metal cutting discs)
4) Soldering iron (25W should be enough)
5) Hot glue gun (super glue, optional)
6) Tool to open up the old battery pack (I ended up using the Dremel)

(a nice site to read-up on li-po conversions: Lithium-IonBatteries.html)

Its really simple, so...lets begin!

Step 1:

First thing first...

You need to determine the voltage of the pack you have on your drill.
This should be  printed on the pack itself.
My pack was a 7.2Volt one (using six Ni-Cd sub-C cells).
So it makes sense to use two 18650 lithium batteries (at 3.7V nominal voltage each)

So we need to replace the old dead Ni-Cd cells with the new lithium batteries.

First of all we take the old battery pack and pry it open.
Some are easier than others. Some even have screws but others (like mine will require a Dremel)
Try not to do much damage as we will need to put the bottom half back on.

The only thing we will need from in there is the battery pack contacts and a small plastic piece that holds them.
Discard the old cells properly (and be careful of any toxic acid residue on them)

Step 2:

So, you are now ready to put the lithium battery holder inside the pack.

Using the Dremel we cut a hole on the bottom of the pack housing and place the holder inside.
Securing the holder with hot-glue and super-glue is essential. 

After that is done we solder the wires to the end contact tabs (OBSERVE THE POLARITY!!!),
and secure the assembly inside the other half with some more hot-glue and super-glue combo.

A this point one should check that the drill works(before putting the two halfs together).
It should work, provided the batteries are chareged and the polarity is correct

Step 3:

All that's left now is to put back together the two halfs of the battery pack.
We do that with some more hot-glue / super-glue combo, and test everything once more.

THAT'S IT... you now have a lithium powered cordless drill !!!

I suggest you get two sets of 18650 batteries, so you can have one set in the drill and one in the charger at all times.

Leave your comments and suggestions at will !

Enjoy and have fun!
Bill Geo

Step 4: 2015: Time for a (power) Upgrade

So after some more use and testing of the drill I found that the current the 18650 batteries can deliver

was enough to drill plastics and soft metals (like brass and aluminum) but the drill struggled with anything more

demanding (even dry-screwing large wood-screws in MDF)...

It was time for a power-source upgrade!

So a 2S 3000mAh Li-Po battery with a 40C discharge rating from my quadcopter project was used instead.

The case was cut to accommodate the larger size of the pack, and the added weight gave the drill a nice balance.

A voltage monitor (again from the R/C world) was added in the back to keep an eye out for over-discharging

(even though the drill is pretty much useless before the voltage drops to any dangerous level).

The difference?


Lots of torque and excellent battery life.

I would suggest to anyone that wants to try a li-po conversion on a drill to go for this type of battery-pack.

Though a mod that uses one or two paralleled 18650 cells will be good enough for a screwdriver or a low-power drill.

NOTE: it goes without saying that the Li-Po pack should be charged with an appropriate charger,

and the voltage level monitored regularly to avoid over-discharge.