I work in a truck equipment shop, when Im not hanging around the bike shop
The new LED tail lights used on trucks might be of use. A stop/tail/turn light could have a stedy burn with a brighter flash. They can be easly seen in daylight. There not cheap, about 30 bucks. and then you need power. Some have built in flash circuts on the stop that will flash 10 times quickly then stay on. some will operate down to 6 volts.
As far as power on the run, I have used my SON Dyno hub to charge batteries for a CD player when riding so it should work for your tail light batteries
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Bentbaggerlen
"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." - Arthur Conan Doyle