Juha
"One question: what kind of AA NiMhs do you use?"

See this site http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM there was a pointer to it from http://nordicgroup.us/s78/. Steven M. Scharf the author of that site suggests an ‘amp hour per $’ analysis. I have more money than time so I bought the Powerex 2200s.

RainmanP
“but the prospect of trying to get 12 or 24 batteries charged every night had me scratching my head”

My charger has a place to plug a battery pack in like people use on remote control cars. It can do up to 12 ‘AA’s at a time. When I built my battery packs I used the same plug (available at Radio Shack with the remote control car stuff) so I can just plug all 12 in at once. I was a bit concerned about charging too so I decided to build 3 packs, charge 1 at night and one during the day while I am at work . I really only need both battery packs in mid December (I hope).

“I fashioned a hood from black electrical tape that keeps water from falling right into the vents but still allows for ventilation”

Thanks for doing the research on the Optronic lights, I was watching your reports with great interest. When I saw your picture I ordered them right away. With a handle like RainmanP it is no wonder you would worry about water in your lights. I did notice your hood and gave it some thought, but haven’t acted as yet. I started to do something and then decided that if it can hang under the bumper of a car open like that why not on a bike. But I haven’t made up my mind either way. Are you getting much heat buildup?