The driver isn’t perfectly circular. One side is flat to hold it in the correct orientation and prevent it from spinning when the retaining ring is tightened.
It also isn’t easily replaceable since the driver was designed specifically for this light. I don’t expect generic drivers to fit. However, it should be easy to reflash if desired. It just requires unsoldering a couple wires and loosening a retaining ring to let the driver come out.
I’m not sure what your saying about the battery. Do you mean a battery capable of 9A continous? That’s kind of irrelevant. I would just use a good middle of the road high drain and high capacity cell like the 30Q or VTC6 3000mah.
A really high drain cell like the VTC4 2100mah or 20S is probably not needed.
You could probably use a high capacity like 35E or MJ1 and still get decent turbo output along with reduced heat and extended runtime.
Unless the lens has changed without me realizing, the beam should have some decent flood to the side due to the frosted lens. You can also polish the lens to remove the frost and make it more throwy.
Au scratches pretty easily, but I’m sure the hand feel is nice, and the thermal conductivity is superb.
As a much harder alternative that also takes a very nice polish, how about an FW3WC (Tungsten Carbide)?
On the other end of the scale, the FW3Mg would be roughly 1/3 lighter than the FW3A, yet still has pretty decent thermal characteristics. Be careful around open flames, however.