Replacing the “non-replaceable” battery in a Phillips SonicCare™ toothbrush
Don’t you hate it when a $140 gadget is rendered useless by the failure of a $2 part? Yah, me too. Well, it turns out you actually can replace the battery in these devices, and very cheaply at that. It’s not a difficult job, and it extends the life of an expensive gadget by years.
Some key details to this job are found in the comment thread on the instructable. Here’s a summary of the information I found useful:
I used a NiCd replacement, rather than a NiMH as some suggest. The charging circuit is designed for NiCd, and since the original lasted 5 years, going with the same type again seems wise.
Removing the retainer pin on the side without breaking it can be tricky. Pry gently with a thin screwdriver from the edge that is the “long side” of the trapezoidal-shaped pin. If you break it, that’s okay. It isn’t critical, it’s just nice to have.
Extracting the guts from the case can be difficult. Don’t pry with a screwdriver- you’ll destroy the plastic shell. Instead, after removing the retainer pin on the side, grasp the collar (with brush head removed) firmly and rock it back and forth. You’ll see a small gap form under the collar (maybe 0.5mm). Then tighten the collar down to close the gap (as much as you can without over-tightening it. Repeat that procedure of rocking and tightening until the case comes off. Be patient. It took me 10 or 15 minutes and my hands were sore by the end.
You can buy replacement 4/5A batteries with tabs welded on, just like the factory. However, that means resoldering to the PCB, which will make replacement harder next time. Desoldering the original battery without overheating all the surrounding components was the hardest part of the job, and I don’t wish to repeat it.
When reinserting the guts into the case, lubricate the new connection wires on the battery with K-Y. They stick out further than anything is supposed to, and will rub on the case during reassembly. The lube will make it go back together much easier, and reduce risk of damaging the wires or solder connections.
Here’s the end result- the battery has been replaced with an off-the-shelf 4/5A NiCd, and wires have been run to the old battery’s PCB mount points. This will make it easier to change the battery next time!