As the batteries in my Sonicare toothbrush have died a slow death, I’ve been looking for a way to replace them. P. Flindt’s Philips Amazon review of the Sonicare 4100 finally provided a promising solution:
Since the warranty expired, I took a Dremel tool to the Sonicare and opened it up. To my delight, I noted that the batteries employed by the unit were two standard, albeit unbranded AA NiCad cells. I removed and replaced them with two 600mah Sanyo cells, closed the handle and sealed it shut with silicone. It’s been over a year now and my Sonicare is working as well as it did the day I bought it.
Hearing the magic word Dremel, I resolved to spend a bit of Sunday afternoon in the basement seeing if $5 of batteries could save a $50 toothbrush. Cutting through the mid-line groove of the handle took a few passes to gauge the 1/8″ depth of the plastic. The top joint, inside the threading for the brush head, isn’t easily reached for cutting, but came apart with a twist of a screwdriver from the side just below.
Inside, the unit is quite densely packed. From the base, there’s a charging coil, the two AA NiCad batteries as described, and another coil to drive the head, all covered with a small circuit board. And it’s quite solid: the whole thing is cemented into the back of the handle with a hardened Soylent Green epoxy. The batteries were not only soldered to the board and each other, but mired themselves in a good 1/8″ of epoxy.
Cutting off the portion of the back housing attached to the batteries made them more accessible. But even after drilling out some of the epoxy, they were still firmly attached. Faced with the remaining tasks of detaching the batteries, soldering in a new set, and resealing the handle and its new battery door, I admitted defeat to the integrated obsolescence of Philips’ engineers. I’ll be buying another one because it does a good job and lasted a healthy six years, but still shaking my head at the design.