Well it all depends on what you mean by powerful.
- There's the Klarus RS1A that uses AA batteries and does 210 lumens at max output. Charging is done on nimh with an USB cable. However there's no variable ring.
- There's the Nitecore MH1A, that can use AA alkaline or 14500 lithium. It's more powerful than the klarus (550 lumens with a 14500), but charging is only done when using the 14500. No variable control ring.
- There's also the Nitecore SRT3, which uses all kind of batteries including AA primaries and 14500. 550 lumens with a 14500. There's a variable ring on this one. Howeverr the SRT3 is not a rechargeable flashlight, so you'll have to buy a charger.
