Down near the end, the poor thing barely gave one brushing after an overnight charge.
While I was dismantling the case, I charged the last two new-old-stock NiMH cells:
They arrived the same five years ago as the deaders in the toothbrush, but haven’t been used in the interim and charged well enough. The NiteCore D4 charger arrived after they did and isn’t really intended for 2/3 AA cells, so I used short brass tubes to make up the difference. I should have used the 300 mA low-current charging option (press-and-hold the Mode button for a second), although it didn’t overcook them at 750 mA.
The process went pretty much as before, with the new cells soldered in place atop the PCB:
And the PCB tucked back into the case:
I applied a solder bridge to the BLINKY pads, which seemed to disable the blinking and turn the LED on full with the toothbrush in the charger. Without waiting for a full charge cycle, I sucked the solder off the pads and restored the previous blinkiness.
A few strips of Kapton tape and it’s back in operation:
The first charge lasted for two weeks, so things are looking good again. When the stock of knockoff replacement brush heads wears out, it’ll be time to get a whole new toothbrush … even if the batteries aren’t completely dead yet.