Went to start my car (1997 Toyota Camry) which was running just fine the day before.
It didn't start, as the battery was drained. It took forever to charge back up. What would cause the battery to do that?
There are three common causes for this:
took forever to charge it back up
I believe the third issue applies.
For the first, the solution is to pay attention when leaving the car: check lights, radio/music player, any consumers plugged into the lighter socket.
For the second, you have to check your wiring by a professional. Beware this type of fault can lead to fire.
The solution to third item is to replace the battery. You can do it yourself or you can ask a professional to do it for you.
I will add that any electrical fault in the wiring will lead to a failing battery. A good indication this is happening is when a fairly new/good battery suddenly starts to lose its charge.