repair - electric shaver battery cloning

Last update: Tue May 19 22:13:22 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. After measuring the shaver sends 30 pulses before giving up an cutting power.
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 1: cell replacement

Just replace the Li-Ion cell in the battery. Regular 18650 3.7v 1200mA. But where's the fun in that? Btw I will do that after I complete solution 3, but I don't want to risk killing the last barely-working battery I have at hand: I need it for the tests.

Solution 2: direct motor drive

Yeah, just measure how much amps go in the motor and drive it? Motor is a Weilong FF-337PA, DC 3.7v at max 0.8A at full load for 6800 RPM (as per datasheet). But let's call this "last resort" solution in case I blow up the whole thing.

Solution 3: battery emulation

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

Sense the 1.2v (do that with ~~an opamp~~ a comparator 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

WORKING circuit to detect signal with LM311

2 evenings discovering Comparators after noticing that it wouldn't work with LM358 (OpAmp) and it worked. Pretty happy to have discovered that puppy at the bottom of my "opamps & comparators" drawer, and happy first experience with comparator. And Mr. Dave Jones puts it as the first of the Jelly Beans comparators!

Driving the 1.2v from MCU

Use a 1.2v voltage reference (ICL8069) and drive it with a npn-transistor (or mosfet) should work: simulation on falstad.com.

Source code

PCB and schematics:

https://github.com/AlanFromJapan/pcb-design/tree/master/hatteker-battery-faker

MCU (ATtiny10) code:

https://github.com/AlanFromJapan/alanarduinotools/tree/master/Attiny10/Hatteker_battery

Pictures

Links

Helpful sources

Inspiration

All content on this site is shared under the MIT licence (do what u want, don't sue me, hat tip appreciated)
electrogeek.tokyo ~ Formerly known as Kalshagar.wikispaces.com and electrogeek.cc (AlanFromJapan [2009 - 2026])