This instructable deals with replacing the Ni-Cd battery pack in 15+ years old dremel Free Wheeler. Despite its age it's a capable little tool the first job I used it for was cutting the outer roller races from the rear swinging arms of a citroen CX. As it is my father's and he told me to change like for like that is what I've done. There is however plenty of space in the case and it could quite easily have accommodated a 1500mAh 2s Li-po the charging board and a new electronic speed control board, but that's not what he wanted.

An option that has only just come to my attention is there might just be space for a pair of 18650 Li-ion batteries and the necessary charging and speed controller boards, something I am adding here as a reminder to myself for next time.

Step 1: Disassemble

Disassembly is quite straight forward unscrew the chuck and the top locking collar. The rest of the case is held together by 4 screws these had a torq head and a straight slot, once removed the case just lifts apart

Step 2: Inside

The inernals of this dremel are very straight forward. The chuck arbour is mounted on a pair of ball races with a direct flexible drive to the motor, the contacts on the motor clip onto the control board this consists of a 3 position switch off/charge low & high speed. I already knew from the old spares list that the battery was a 5 cell Ni-Cd hump pack but was unsure of the exact size of the cells they turned out to be 4/5 sub C, had they been full subC the next step would have been easier. Also high and low speed are unfortunately achieved by having a tap at 3 cells for low speed this is not good for the life expectancy of the battery pack. At the bottom of the case is the charging socket.

Step 3: The New Battery

My father was insistent that he wanted like for like for replacement if possible, or at a pinch would have gone for nickle metal hydride cells instead of Ni-Cd.

I found a company online www.batteriesplus.co.uk that supplied tagged Ni-Cd cells of the right size (in hind sight I should have paid them a little extra to make a welded pack up)

Using the old pack as reference I arranged the cells in the correct order held them in place with a rubber band then rotated the cells so the tags needed the least bending to make contact. Using a strip of thin card as insulation to avoid burning the plastic sleeves of the cells I then soldered the tags together.

I then cycled the new pack several times using a commercially available battery charger. I've since made a lead to use this charger with the dremel instead of the so called trickle charger which is nothing more than a wall wart.

Step 4: Tag Salvage

No photos available as this entailed tool abuse. I had to salvage the connector tags from the old pack, I did this by working a shall wood working chisel between the tags and the battery case deforming both in the process then once positioned tight against the spot welds a sharp blow with a mallet cut the tag free.

The tags then needed straightening out, and the weld dimples filing off. They were then tinned and soldered into place on the new pack.

Step 5: Refitting

The rubber band was replaced with packing tape, and new side plates cut from a thin card box and stuck in place with hot glue. the new pack was then placed in the case the cables refitted (note the cables are made with next to no free play the tags had to be soldered in the right place in the right orientation for the his to work)

Making sure the switch was in the off position the motor and drive assembly were fitted in position and the other half of the case refitted.