Good job on having a backup roadrunner1659 (2 head lights and 2 rear lights). Although you can usually tell when the batteries are dying, you never know exactly when it's going to happen and you sure don't want it happening at the start of a long commute on city roads at night. And "more lights" is probably a better option than just "more batteries".

Since you're commuting after 9 pm on Saturday nights, "being seen" aspect of lighting is probably a big issue for you. For the money, I don't think you can get any better than the Planet Bike Superflash for a rear blinky. I use the 5 LED CatEye up front in flashing mode and have been happy with it, but I use several types of lights to actually light the road.