Honda Prelude

Check to make sure all of your ground wires are secure. Next check to see if the battery might just have a bad cell. This happens more often than you think for Hondas because they have such small batteries. Also, if you have replaced your stereo recently, this may effect things. The power and ground leads for the stereo do some pretty crazy stuff when they are touching things they aren't suppose to in the dash. Good Luck.

Double check to make sure nothing has been left on, also check the courtesy lights in the interior, glove box, trunk etc.. to make sure they weren't left on accidently.

Then, if you have a test light, I'd disconnect one of the battery terminals and place the test light in series with the connection. (ie.. tester to battery and cable to tester) The current should not be high enough to light the test light when it's connected this way. If it does light up, try disconnecting the wires going to the alternator, if it goes out you probably have a bad diode in the alternator. A bad diode can have a pretty good current draw, which can drain your battery down in a few hours.

If it didn't light up when you first hooked it up in series then you can hook up a mulitmeter inline (reading amps) in series (in place of the test light) to get an idea of how much current the system is drawing. It should be no more than around 75milliamps. If it's up over an amp or so you can start pulling fuses and relays one at a time (putting back the good ones as you go) while making note of the reading on the meter, when the meter current draw drops off, you can isolate which system the fault is in.

Hope this helps