I have some spare voltage converters if anyone wants, with 36/48 volts input and 5v/80w output. they can be connected in series to make 10/15V output, which is very good for LEDs because most power LEDs are rated at about 3.3V so three in series makes 10v... about 5 cm by 5 cm by 1 cm, 50 g
also it means you can attach regular bike lights to them because 5v is the same as 4x aa/aaa batteries.
I am thinking of using one 12v/10w halogen headlamp and 2 really cheap flashing back lights from eBay wired in series to make 5v...
I have tried the converters at 24V and the output is 5.03v, but I don't have the data sheet, they are rated at 48v in, similar ones can do in between 18 and 70 V but I'm just saying in between 36 and 48 because I don't know. £3 each
including postage, as many as you want