They don't even want you to use 3 rechargable cells with the M8/Sabrelight LED. I can't imagine that 4 alkalines will do anything but destroy the circuitry.
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I have to agree with Doug, you stand a good chance of frying something. If you want to hot rod it, try swapping in a 5 watt instead of the stock emitter and THEN mess with the battery supply and electronics.
It would be neat to see the biggest, baddest "recoil" type light.