So I just bought a new mountain bike and have been riding it around the neighborhood and some local park trails. I would like a headlight for it but they are plenty expensive. I thought about using a multi-LED flashlight with an auxillary battery pack to get more time out of the light.
I have a small 14 LED chinese made light that runs on 3/AAA batteries at 4.5V. It is plenty bright but I don't think it will last long.
I also have a Maxfire Xenon Rechargable that runs on a 2/3A x4 Nicad battery pack at 4.8V but only 650mAh.
My thinking it to have a higher capacity external battery pack made that will be rechargable. Then wire the battery pack directly to the light which will be secured on the handle bars.
I did this with a qualitychinagoods.com 7watt luxeon. I cut the tube down, drilled a hole in it, removed the resistor, and linked it to a 3xAA nimh pack Has a really nice spot, and seemed to work well. since then, I moved on and built a 100x5mm led light that is close to HID levels, and a 30 watt hid lamp that was wicked bright until I sold it. The thirty watter was fantastic... All my friends just turned off their lights when they rode with me....
I sorta did this too, as I don't need a waterproof system, and thought that the desired output could be had for under $200. I started with a Cateye 2-C headlight for the QR mount and case capacity. I subbed in a Mag. Whitestar 4-D bulb, and wired across the battery terminals, leaving a pigtail out the back. I then put two sets of 4 Nicad A-cells in parallel (because they were cheap, $1 clearance for a car phone pack using 12 of the A-cells) in a H2O bottle, running a wire out the top with a mating connector to the light. The heat from the bulb was OK in the Cateye, and the beam a quantum leap forward, but I wanted an LED flood for close in and long runtime. So I cannibalized the head of an ACO 8-LED, 3 AAA light and soldered another set of wires to the back and velcro strapped it to the top of the Cateye in a block of foam, inner tube rubber boot zip-tied to the back for decent environmental protection. I then ran wires into the light, with a switch in line, to the same power for the main light, through a stepdown resistance (brake light bulb worked good) and had near and far lighting with independent on/off control. Then I finished off by upgrading the 8 LED's to 50 K JELED's, which makes the LED light a decent light by itself in low light conditions at moderate speeds. Total cost was around $15 including the headlight I started from.
The LED pulls about 220 ma, the incan about 600 ma, and my current pack is 2800 mah, so you can figure the possible run times depending on what is turned on. At least 3+ hours with both lights, WAY more on LED only, and those batteries are quite archaic.
If I add the Dorcy 1W Luxeon headlamp (3xAAA) to my helmet with velcro strap replacing the head band, and all 3 beams are on, I like to call it "high noon at midnight", on a budget! I was planning to drill the battery cap on the headlight and solder on to the battery holder so I could run a remote pack, either at the back of the helmet for balance, or of higher capacity in a pocket on a longer lead. Just haven't been using it enough to get motivated to finish that part.
I also just tried this the other day with a Royce Union 2C bike light. The light output was dim and the beam horrable so I took a 5 cell radio shack bulb, wired in a new switch and attached a 9.6V remote control car battery pack to the underside of the top bar. The light output was fantastic for about 5 minutes until the heat of the bulb melted the reflector to the point that the bulb could not make contact with the terminals and fused the bulb to the reflector. So now I am using a ROP with a 6 cell bulb in a $2.99 maglite flashlight adapter for the bike which is still ok but not as good as those first five minutes of the modified bike light.
When you don't want spend extra money for a special bike light, I would go with a Trilux light. It should have 2 brightness levels. So you can use at streets the low level and when you will need more brightness only one click and wow.
The advantage is, you can use it as a bikelight and as a flashlight.
My Trilux Magmod runs 1 hour 30 minutes on high and more than 6 hours on low. With 7spare cells you can ride your bike the whole night.