I emailed Dinotte once and they really got cranky about me suggesting that I hook a 7.2v lithium pack to the 4AA taillight. They claimed that the two lightheads were different and that the 4AA one couldn't take the extra voltage.

Personally I kind of doubt it, because even after I said that I'd put a buck converter in line to drop the voltage to the same as the AA cells, they said I'd damage the light. I think either the person that sent the email was a sales person who only knew to say that and not any engineering, or they just wanted to sell me the LiIon light instead of having me mess with the existing light.