I'm somewhat old and very crotchety. I don't believe in index shifters or cassette hubs and currently I don't even have a smartphone. I use a wind-up watch and a fountain pen. I wouldn't use the newer tech if it weren't really noticeably better. In this case, it is.
First choice: cheap Sanyo dynohub + Busch & Müller lights. I've got four bikes running this setup. Seriously, it's worth the initial investment -- once you get a dynohub wheel, you'll never think about batteries again.
Second choice: USB (I like a Cygolite Metro 600, for the 10+ bikes that don't have dynohubs).
Third choice: rechargeable AAAs.