Two bikes:
1) Recumbent: Front two lights are Nightryderz. I recharge them about every weekend, just to be on the safe side. I've used one every morning for over two weeks without noticing any dimming, and I don't always run both when commuting, so there's a backup. Tail lights are all rechargeable AAs. I have two small buckets in the house, one for 'dead' batteries, and one for charged batteries. When I get 8 in the dead bucket, I put them in the charger.
2) Velomobile: This has a 12 volt system with a battery pack that runs the whole electrical system (headlight + highbeam, tail light + brake light, turn signals, and horn). It's good for a week of commuting, even in the winter when I'm using for both to and from work. I charge it usually friday evenings after work. If I go for a long ride on the weekend, I may charge it again sunday before the work week. I will be ordering a spare in a few weeks.