Actually, the AMC7135 chips are rated up to 6v and the voltage range of the Nanjg (and nanjg clones) is technically rated at 3v-6v. Depending on where you buy them the specs will show different ranges but usually between 4.5v and 6v max. Many here run 2*3v primaries with the Nanjg drivers with no issues. They will get hot because they are transferring the excess voltage to heat but it can and has been done by many. Some with worse luck than others. Because the AMC7135 is rated at up to 6v you will be pushing things and therefore increasing any chances of failure. You can NOT run RCR123A or 16340 Li-Ion (3.6-3.7v) as doubled they will be 8.4v fully charged. 3v primaries should be ok but be aware that you run a higher risk of failure.
Yes, aware of the 6v tech spec on the chip and some guys run them that high, not definitely not your common use, and the drivers are not typically spec'd for 6v max.
So in a pinch or emergency I could pop two CR123's in and use it for a little while, but it is pretty much maxing the thing out and increase the risk of catastrophic failure.
where I “accidentally” (I forgot) used it with 2x18650, and it killed the drop-in. From post-mortem, it appears that the emitter was what failed, and the theory that I’ve seen was that the driver went into direct drive, passing the 2x3.7V through to the emitter, which killed the emitter?