I've been picking brains over on the C&V forum about my setup and by their suggestion I've come here to see if I could get a little more input.

I have an old headlight that I have put 25 leds in, replacing the original incandescent bulb. It's 25 leds soldered together in parallel on a radioshack pcb. I have an sram dyno-hub on the bike now that I want to power the light with. When I was initially putting this together my plan was Dyno-hub > bridge rectifier > headlight > 4 AA rechargeable battery pack.

Now, I've been told that I need a capacitor and that using a battery pack in place of a capacitor is not a good idea (something about exploding batteries).

From what I understand, I could just wire it up with the bridge rectifier and be good to go. However, I would like to have the battery pack in there to keep the light on when I'm not moving.

What is the right/safe way to implement the battery pack to keep my light on while not moving?