Can Malkoff drop ins such as M61w and M61n be used with rechargeable batteries imr123?

I’m thinking about getting either 3000k or 4000k version but I hate non rechargeable batteries

Also, the light seems to run direct drive under 3.4 volts

So I figured if I use 2 x 3.7 volts that should keep it in constant current drive

The description says it can run from 3-9 volts

Is this correct?

Yes.