I have a spare LED from my 4D MagLed (just put in a terralux) and a spare 2C Maglite, the LED can take 6V, but how much more voltage can I put into it?
The LED itself takea around 3-3.7v depending on current. The drive that regulates power from the batteries can take 6v, and is a buck circuit, so anything under 6v is fine, but anything unvder 3v probably won't even light up the LED (I'd stick with 4.5-6v for the voltage range).