What do any of these posts have to do with the question Nute asked in the OP?
Nute -
Ignore everything everyone in this thread (except crazyspaz) has said. That includes the manufacturer. Assuming you're talking about the Survival Laser in your signature, I don't think they really make their own driver and I'm not sure they actually understand how their driver works.
I think I do - it's a 300-500 khz switch with a relatively low value inductor, small caps, but an IC that on the datasheet can handle a bit over 20V of input. Hence their comment that up to 18V is fine.
It's not.
At three cells of input, the driver will still work, will have the same output current, and it won't burn out or catch on fire. But with the relatively low frequency of their IC, the anemic inductor, and the relatively small caps, you're going to end up with bad voltage ripple.
If my math is correct, you'll probably triple the ripple, by going to 3 cells instead of 2. It will still work, and your diode will still see the same average current, but it will take a much bigger beating in the process. Again, SL probably doesn't know this, and they've probably tested with three cells and saw that the diode worked, so they think it's fine - but it's not.
