The rule of thumb is that you need to derate battery amp-hours by 50% for real-world applications. There are two reason for this -- first, most batteries don't last too long if they are completely discharged, and second, the ratings are usually for a 20-hour discharge; faster discharge usually delivers less power. So with a 37 watt bulb and a 3-hour commute you need more like 18 Ah of capacity. That is beyond commonly available NiMH battery types; I'm not sure where you'd get that capacity. I would not recommend running rechargeable batteries in parallel. Basically, there are two things that destroy batteries -- overcharging, and complete discharge. The more individual cells you have in your pack, the more likely that one cell will be overcharged or completely discharged without you noticing. Once that happens, the pack is toast.

The pack that multibiker linked to looks like a good starting point. Batteryspace is the only place I know of that sells smart chargers for NiMH packs of more than 8 cells. As the number of cells increases, the smartness of the smart charger has to increase as well, for the reasons noted above. Note that this pack is 12 cells. One problem with NiMH is that the voltage declines pretty sharply as the cells discharge. While NiMH has a nominal voltage of 1.2 volts, a fully charged cell will be about 1.4 volts and a cell at the limits of usability will be about 1.0 volts. So this pack delivers a minimum of 12 volts, an average of 14.4 and as much as 16.8. For a halogen bulb rated at 12v this is actually a pretty good fit, as halogen bulbs are dramatically more efficient when over-volted. Over-volting reduces bulb life, but typical life ratings are in the thousands of hours and I always break them by crashing or dropping them before they burn out. FWIW I have a 12-cell NiMH on my bike with 12V halogens, and I use the BatterySpace charger.

So this pack gives you a "budget" of 9.5Ah. I would work backwards from there. Derating by 50%, a three-hour run time puts you at about 20 watts. For my money, there are only two bulb types worth using on bikes, the MR16 which is 2" in diameter and comes in a variety of wattages and beams, and the PAR36, which is 4" in diameter and comes in 14 or 25 watts, flood beam. For the MR16 the consensus is the Optronics housing is the way to go; I use this housing: http://www.northerntool.com/webapp/w...4&storeId=6970 for my bike with the PAR36. Both of these housings are automotive, in answer to your question "Is anyone else on the thread still runnning an automotive bulb solution?" although probably not the answer you were looking for.

You'll have to figure out what combination of bulbs to spend your 20 watts on. What a lot of people do is have one flood light and one spot light. There is not a whole lot of choice available in 10w bulbs, so your best bet may be to use 2 20w bulbs and wire up a switch so you can switch between them. Depending on your commute, it also may make sense to use a 10w or 14w for normal conditions and the 37w you have for high visibility times.