Ed-

I bought a rechargeable adapter kit for a G2 and have mixed feelings about it.  The rechargeable surefire batteries have the same power and comparable runtime, but they lose charge very quickly.  If it's going to be used every day, or at least a few days in a row for 30 minutes a day or something, go for it.  Otherwise, you'll probably find yourself having to charge the thing right before you want to use it each time.  One advantage to the Adapter kits: you can unscrew the extender and pop in a set of 123 Lithium cells when the battery pack goes down.