Back when I got a Philips Sonicare (on the recommendation of my dental hygenist, after a particularly nasty bout of plaque removal), the battery gave nearly two weeks of service between charges. As shown in that graph, the runtime gradually faded away to two days, at which point I decided it was time to tear the thing apart and see about replacing the batteries.
The instruction manual tells how to dismantle the case and extract the NiCd battery for recycling:
Please note that this process is NOT reversible.
Well, there’s a challenge if I ever read one, but Wouldn’t It Be Nice If you could take something apart, unplug its defunct battery, install a new one, and button it up again? Then you wouldn’t be forced to buy a new $70 toothbrush, which probably explains everything… and I suppose the replacement battery would cost $40, even if it were a pair of AA cells.
For reference, the instructions (clicky for more dots):
As predicted, suasion applied through a small screwdriver popped the top end of the case apart, but the remainder required concerted prying and muttering. The case halves mate with a tongue-and-groove joint that’s either sonic welded or adhesive bonded to form a watertight seal all the way around, to the extent that they suggested cleaning the thing in a dishwasher.
Eventually, though, it came apart:
The “motor” (actually, a solenoid that couples to the magnet on the brush stem) is firmly potted in place (on the right), as are the NiCd cells and the charging power pickup coil at the base on the left. The potting compound seems to be a clear epoxy, rather than a compliant rubber, and it doesn’t bond to the case at all. It is, however, a perfect fit and doesn’t pop loose without a struggle; their instructions will definitely break the PCB.
Seen from the other direction, six connections join the PCB to those immovable objects. The four pins (on the far left) go to the solenoid and the pair (just to their right) to the battery:
A few dabs of desoldering wick suffice to free the pins and release the PCB. Mercifully, the potting compound surrounding the charging coil slid out easily, as they (inexplicably) omitted a mechanical lock molded into the case:
Removing the NiCd cells required considerable prying, as described in the instructions, that en passant damaged their cases. I think if you weren’t paying attention, you could easily rupture a cell case with the screwdriver and spatter the area with potassium hydroxide, perhaps shorting the cell in the process and producing rather more excitement than most folks expect.
A closeup of one cell; the other bears similar damage:
I snipped off the cell tabs and applied them to the new NiMH cells. A bit of closed-cell foam between the cells and the PCB cushions the assembly:
Stacking more foam snippets under the cells filled the space left by the potting compound, then soldering the solenoid pins held everything together:
A wrap of clear adhesive (rather than the obligatory Kapton) makes for a tidy joint that probably won’t last very long, but it looks much the way it did before the operation. The case is no longer waterproof and won’t withstand the dishwasher. In fact, I must now store it with the brush end downward to keep the last few drops out of the handle.
There’s an interesting solder jumper on the PCB that I didn’t bridge, but the next time it’s opened up I’ll apply a dab:
The alert reader will notice that I’ve replaced 2000 mA·h AA NiCd cells with 600 mA·h 2/3 AANiMH cells, without changing the charger. The power transfer through the inductive coupling drives a trickle charger at about one hour of recharge per brushing, so there’s not much danger of overcharging the cells.
Now, to discover what runtime fresh cells deliver. This calls for another slip of geek scratch paper in the bathroom.
The Smell of Molten Projects in the Morning 
“Dynamic cleaning action drives fluid between teeth”
Sadomasochism or Chinese water torture commercialized?
I have no clue what they’re talking about or why that’s a Good Thing. AFAICT, it’s just an awkward buzzy toothbrush that does a better job than I do of keeping the back of my lower front teeth clean. Works for me, anyhow.
Shameless product promotion “Finnish rye-bread”.
Good for teeth and contains a plenty of dietary fiber. Let it dry and it gets even better and won’t mold.
Looks yummy!
I’m still baking a loaf of our high-traction bread about once a week. Increase the bread flour to 1 C, drop the wheat to 3 C, and it’s slightly less durable.
We did sourdough bread for a while, but had trouble keeping the starter running. I should try that again sometime; maybe we have more durable yeast in the air around here.
I had the same toothbrush and tried a similar transplant (I used AA NiCds instead of Nickle metal hydride). I simply could NOT get the thing sealed again… despite my best attempts at not getting the brush body wet, H2O still creeped in somehow, and corroded everything, making me a very Sad Panda :-( And I HATE Pandas. I tried to seal the thing with generous application of RTV, b.t.w. The new Sonicare replacement has a LiIon battery, and is easier to open to take the battery out.
After my failed attempts to repair, I found several Instructables that gave more details on how to replace the cells. Worth checking out…
– Steve
I expect creeping moisture will be its downfall, as that nice tongue-and-groove joint is no more.
Eking out a few more years should satisfy my repair compulsion, after which I can get a fancy new brush with a completely new set of challenges!
The ones that light my butt rephrase a repair I’ve described in some detail, while listing my post as a “reference”… [grin]
Several years ago, we had a run of Sonicare brushes with the same failure mode. The switch was a rubber covered hole in the case over a switch on the PC board. After a while the rubber cracked so moisture could leak into the electronics. The first symptom was crazy behavior. They usually recovered if left unused long enough to dry out.
The fix, not really satisfactory but none the less amusing, was to stretch a band cut from the thumb of a rubber glove over the button.
Y’know, there’s another product you could use: just slip the whole case inside! [grin]
ummm… …
The old girl may wonder why we have those things around!
>:-)
{wife}”For the Sonicare, SURE!” {/wife}
I think it’s best this thread stop right here… [wince]
BTW, SAVE those NiCads, Super easy to rejuvenate!
I saved an ancient Ryobi 18V and it’s AWESOME!!!
NiCad is a great cell…
Never had much luck doing that sort of thing; the Bulging Brains suggest that you’ll clear the worst of the crystallization and the rest will continue to weaken the cell. I’m certain there’s anecdotal evidence on both sides… [grin]
Sure, but maybe my excellent result was due to the home built Relay Charger re-con effects. It’s much
like the renaissance charger but I built mine under
$20 O.O
NiMH’s like it too, everything but LiIon works good with it.
The only drawback is I never did build an automated charge tending circuit.
Blew up a silver cell, it went off like a .22 cal round!
PS: I save old batteries like you save everything else, Ed!
My original(!), before-model-numbers Sonicare just died the true death yesterday after my trip to Nevada. I tried to get the case halves apart but they’ve become so brittle from the decay of the flame retardants that they shatterd into a dozen pieces. After a mere fourteen years! Nothing lasts!
Somehow, I’m betting the replacement I’m about to buy will not still be with me in 2028.
On the original pair of NiCd batteries? Sure don’t make ’em like they used to!
Must be RYOBI lol
In re: that jumper, mine blinks an LED inside the power button to tell you the state-of-charge. If yours doesn’t, that’s probably what it enables.
This one blinks when it’s about out of gas, one or two brushings before it gives off a plaintive buzz…
Much to my astonishment, the tape around the case hasn’t disintegrated: no reason to open it up!
How do the new batteries stand up against the old? where’s a good place to ask a question about an old cordless drill and it’s brushes?
They’re running over three weeks per charge, which is where the old ones started, and seem perfectly happy. I’d hope these last a bit longer, but ya never know.
I may have replaced two sets of brushes over the years, so I definitely don’t have any inside information… [grin]