Ok, did some further research and reverse engineering on this light - pulled the driver out. It's a classic FET+1, using a SIR800DP FET. So this is a high power driver. The max amps/power may be restricted in firmware, but certainly this explains the lack of regulation, and testing results on different batteries.
The processor (MCU) is made by Nuvoton, based on the 8051 (old MCU), but with all the modern advances of on board memory, PWM's, timers, etc. It's got an 18 KB space for code which is good - our typical Atmel Attiny85 has 8 KB, so this is more than double the space. Listing/link to spec sheet here: https://www.digikey.com/en/products/detail/nuvoton-technology-corporation-of-america/N76E003AQ20/8747840
So, guess they copied our FET+1 design but went with a cheaper, unknown to us, MCU, without source code :FACEPALM:
Main pieces, easy to take apart (all good here):
Green NM1, secured nicely with screws (all good again):
Shows access to re-program the firmware via 5 pogo pin type of programmer, driver retaining ring removed (again all good):
Dual springs (good):
Need to de-solder the LED wires, than the driver can be pulled out:
Ok, the main contact board is where the driver circuit is, while the vertical board is strictly the USB-C charging. I've tested the charging on a USB-C wall charger and it works, so it's a real USB-C charger (also very good!).
On the driver board, a few parts look very familiar - classic FET+1 design, even the 4.7 ohm from Batt+ feeding the D1 diode, then to the MCU.
The 3AQ20 labeled 20 pin flat pack part is the MCU. The green wires looks to be the AUX LED in the switch, and blue wire for the switch.
It's not a bad design, fine for max amps, but would have to be carefully tweaked per NM1 color. Regulated amps of course would be much better.
For example, if I had a white NM1 version, I'd first experiment with batteries to find one that max's out at about 5 amps, or just less. If a 35E, GA, or MJ1 gets the results fine, if not, I'd replace the LED wires with longer and smaller wires, like 26 AWG and re-test.
It's not a light to just pull out of the box, slap in a battery, and go.