I use a B&M toplight [back of rear rack] Line [Fresnel type lens turns 2 LED's into a bright line + light up the rest of the taillight]
plus(it runs off hub dynamo) but they also make a battery version.

there the senso feature, option is useful. switch in that mode, it can be left 'on' & will light when you are moving and its not daylight
then turn itself off when you stop. ... for a few minutes (time, longer than stoplights )


On the Lid of the Carradice Cordura Bag I still have the VistaLight I got 20 years ago It Blinks
AA battreies last a long time.

have a Spanninga 2AAA powered taillight on the Mudguard of a couple Bikes ..