Hi there - here is a repair and an upgrade all in one!
I've been using this electric toothbrush for a few years now. Gradually the battery has lost it's ability to hold charge to the point where it needs to be plugged in (or rather placed on the charging holder) every few days. I though I'd try changing the battery (actually 1 cell as I discovered) and see if I couldn't get a performance enhancement at the same time.
As with many of my Instrucables you can either read the steps here or sit back, relax and watch the video embedded here or browse my YouTube channel linked here.
Step 1: Disassemble the Toothbrush
1) Remove the brush head
2) Using a small adjustable spanner place this around the flat of the white plastic part of the toothbrush as shown and twist the spanner anticlockwise
3) After twisting about 30degrees the white plastic should disengage from the main body of the toothbrush
Step 2: Slide Out the Inner Mechanism
Once released the inner mechanism should slide out easily.
Take care not to lose the spring at the bottom of the mechanism (inside the copper coil).
Set aside the main body and the spring - we won't need these until we come to reassemble the toothbrush.
Step 3: Inspect the Inner Mechanism
On one side of the mechanism is the PCB (Printed Circuit Board), The PCB controls the charging of the cell (battery) and also drives the motor. The PCB also has the momentary push button up near the top. Turning the mechanism over we can just see the cell (yellow in colour).
Step 4: Preparation for the Removal of the PCB
De-solder the 4 tabs that hold the PCB and cell in position. 2 of the tabs go to the motor and the other 2 go to the positive and negative of the cell. The negative tab on the cell needs to be bent up to enable the PCB to be removed. Once this is done the PCB can be simply lifted away from the rest of the mechanism.
Step 5: Slide the Cell Out of the Body
After the PCB is removed the cell can be simply slid out of body of the mechanism. I'm not too sure on the capacity of the original cell but it has the number 600 on the outside so I'm going to assume that refers to 600mAh. I'm replacing this old NiCd cell with an Eneloop NiMh cell with a 2000mAh capacity so I'm hoping for a (at least) x3 increase in time between charges (in comparison to the original cell).
Step 6: Spot Weld or Solder Tabs Onto the New Cell
I have a battery spot welder which I used to attach the 2 battery tabs but the tabs could be attached by soldering - just go easy with the amount of heat you apply to the terminals of the cell to ensure you don't damage the cell itself!
Step 7: Slide the New Cell Back Into the Holder
Now it's time to start the re-assembly!
Firstly, the new cell has to be slid back into the body of the mechanism. Carefully align the positive tab of the cell with the slot so that it will line up with the PCB
Step 8: Re-attach the PCB
The 4 joints previously de-soldered need to be re-soldered!
Remember the negative tab needs to be bent 90Deg to enable it to be soldered to the PCB
Step 9: Reassemble and Finish
With the spring at the base inserted into the coil, the assembly can be slid back into the body. Ensure the parts are aligned by making sure the switch on the PCB is lined up with the button molding on the outside of the case. The 2 parts are then pressed together firmly and they should snap together in 1 shot - so to speak.
Initially I found that the toothbrush wouldn't work but I found that it re-energised the internal chip when I placed it back on the charging cradle momentarily.
Now your finished!
PS in the 3 weeks since completing this I've only recharged the toothbrush once - and even then it hadn't fully discharged like it used to do!