2 minute teardown.
I bought a starter kit of eneloop Ni-MH batteries and a wall charger (NC-MQN06U) circa 2010-2011.
HR-3UTGA 1.2V, min 1900 mAh, Made in Japan.
At the time they were all the rage: https://en.wikipedia.org/wiki/Eneloop
Today there are more high-capacity low self-discharge Ni-MH manufactures available.
The wall charger, charges cells in pairs at an advertised rate of 300 mA for AAs and 150 mA for AAAs.
Popping the cover open
A self-oscillating flyback provides and isolated and regulate 4 VDC supply to the charging circuitry.
Charging is managed with an 8-bit MCU EM78P259N
https://www.alldatasheet.com/datasheet-pdf/view/118218/EMC/EM78P259N.html
Charging current is regulated with a pair of ballast resistor providing an equivalent resistance of 3.57 Ohms
The charger briefly pauses charging and samples the cell voltages with the ADC input on the MCU.
When charging AAA cells, the charger PWM modulates the charging current at 50%, to achieve an average charging current of 150 mA.
Gough Lui’s teardown shows an even simpler Ni-MH charger. https://goughlui.com/2013/12/22/review-teardown-sanyo-eneloop-batteries-charger-nc-mqn04a/
