Background

Over the last half a year, my toothbrush (~ €50) lost almost all its battery capacity, going from lasting more than 2 weeks to less than a day. To solve this problem, I decided to try a battery swap, and I’ve described the process below so that you can try it too. However, please note that I do not take any responsibility for accidents that happen while attempting this repair.

Needed materials:

• Screwdriver set
• Knife
• Nail (optimally with the tip of the head removed and filed smooth)
  • The nail should be the same diameter as the hole at the top of the toothbrush.
• Piece of paper
• Pliers
• Lighter
• Soldering iron
• Solder
• (Solder Flux)
• Replacement Battery (HFR28AA-2.4V NiMH)
  • It’s best to first remove the original battery and check the part number to ensure you get the correct replacement.
  • In my experience and reader feedback, this battery has proven difficult to source. If you can’t find a battery advertised specifically for this model, make sure it meets the following criteria:
    • Voltage: 2.4V (2 x 1.2V)
    • Battery technology: NiMH
    • Existing solder tags
    • Dimensions: 55mm × 14.5mm

Steps for the repair (see pictures below)

1. Disassembly

1. Remove the screw at the very bottom of the toothbrush.
2. Insert a knife between the seam between the bottom of the toothbrush and the bottom piece to remove the bottom.
3. Cut the wires from the spool that is now dangling from the PCB.
   • Important: Cut them as close to the PCB as possible, ideally directly at the solder pads.
4. Remove the pin at the top of the toothbrush by carefully pushing it with the nail.
   • The pin is hollow and therefore quite fragile. If using pliers for pulling the pin, be very careful.
   • When the pin is removed, pull the head off its base.
5. At the bottom, you can see two clamps holding the core with the electronics fixed against the outer shell.
   • Both clamps need to be opened by shimming a piece of paper between the outer housing and the inner electronics bay. Do this by first putting a small screwdriver into the clamp and then forcing it inwards while simultaneously putting the paper strip between the outer housing and the inner electronics bay.
6. Push on the top of the toothbrush to slide the electronics bay out from its outer housing.

2. Battery Replacement

1. Desolder the two battery flags from the PCB and remove the battery.
2. This is a good time to give your toothbrush a deep clean.
   • Don’t use water to clean the electronic components and wait until everything is dry before proceeding.
3. Put the new battery in place, stick the tags through the PCB, and (after double and triple checking the polarity) solder the battery flags to the PCB.

3. Reassembly

1. Slide the electronics bay back into the outer shell, but don’t put it all the way in. Leave the solder pads of the charging coil sticking out slightly.
2. Re-solder the coil to the pads on the PCB.
   • The ends are insulated (even if it looks like bare copper), but the insulation can be easily burned off with a lighter.
   • Only expose the end shortly to the fire (~ 2 seconds); otherwise, you risk damaging the coil.
3. Slide the electronics bay back into the outer shell until you hear the click of the clamps.
4. Put the bottom back on and secure it with the screw. Place the head back on and secure it with the pin.
5. Done!