repair - electric shaver battery cloning

Last update: Wed Apr 29 13:23:28 2026

My Hatteker shaver / trimer last replaceable battery died (or close enough). I loved this one, bought a second one: best cost/performance shaver I got. Can I make my own or just make it a wired-to-USB version? Both are ok for me, I don't shave in the shower anyway.

Presentation

Principle

Battery contains a 18650 Li-ion, and some circuitry (a TC4056A for charging, leds/caps). It has 3 pins, that ID as Battery+, Battery- and the third "IN+" as of the PCB. Just plug the B+/B- in the machine and it turns on a glimpse of a second (motor vibes) and immediately stops.

Points of interrest

What happens is that the IN+ is a sensor pin to identify the battery as genuine. Protocol goes like this:

Every 2 ms

Shaver pulls IN+ at HIGH (=1.2v) for 300us

20us of low (turn around time)

The battery then turns IN+ HIGH (=1.2v) for same 200us

Then low until next cycle

If you plug only the B+/B- then there is only the pulse generated by the shaver, un-answered (not plugged!) and the shaver disable itself immediately.
There must be some circuitry in the battery hidden behind the power pins, because IN+ is not connected to anything, but I don't want to risk destructive maintenance (I have one barely functionning battery, it's useful to baseline with a working sample).

Implementation

Solution

Emulate the genuine battery!
Assuming we will make it a wired version, USB 5V:

Sense the 1.2v (do that with an opamp to reach interrupt level of 3v+?)

Catch the interrupt (small MCU)

After FALLING edge, wait 20us, send 300us pulse = need to generate 1.2v pulse and send that on IN+

Avoid brownout when the motor starts (sharp voltage drop on the scope)

Schematics

Source code

Pictures

Links

Helpful sources

Inspiration

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