Having lovingly used my electric toothbrush (twice a day) for at least 4 years, changing the brush heads is commonplace however I've never changed the battery. After 2 years I noticed the power of the toothbrush dropped off after the first 3/4 brushes. Initially my toothbrush lasted 1 week on a full charge it was giving me 6 full brushes (3 minutes per session), which didn't last me a weekend away.
I looked around for the model and where I could get a replacement battery. Having looked through a few tutorials I knew (hoped) I had the skill set to pull this off, at least brush up on my soldering.
The model toothbrush I have is the [Braun professional II], with model "Type 3756" found at the base of the unit. This electronic toothbrush isn't really designed to be repaired so don't think you can just bust this bad boy open and swap out the AA battery. This battery is specialised and soldered into the toothbrush.
Removing the plastic ring from the body
Remove the base battery cover
Years of use can be seen here!
The new battery and the base removed
The inner workings exposed
Desoldering the charging coil
Desoldering and removal of the old battery
The new battery is installed and the charging coil is attached
Battery is working and now needs a good overnight charge
I decided to go with the 1400mAh capacity battery so now my battery should run for longer before it needs a recharge.
The original tutorial can be found here.