What's wrong with my battery?

So I've recently been having a problem with my car battery. It starting acting up last week. My battery light came on and both my headlights and interior lights got really dim. The first time this happened I was experiencing this problem and just happened to roll through a puddle of water and everything went back to normal. What does that mean? Well the next day I bought a new battery and the problem seemed to go away, but no. Just yesterday it started doing the same thing again. My friend told me that it's probably a short, but I don't even know where to start looking. Luckily I've got a waranty on the car battery so I'll replace it, but I don't want to have to keep doing this every week. If anyone has any ideas of where the short might be or what the problem actually is, please help... Thanx

I would have your alternator tested first. The components in the car can only utilize the battery for so long. With a weak alternator it will not be able to compensate. Most parts stores will be able to test the output of the alternator without removing it from the car.

try this when it's running take neg cable off battery and if it dies it's your alt.it is not charging...good luck...

trust me is most likely ur alternator you have a short or is bad you need a new one.

do not do what scrapper says, you'll risk frying your ecu/ecm... go have your alternator tested on the parking lot for free at a local autozone/ advance autoparts

or if you're handy w/ a voltmeter, put the leads on the battery terminals, read the v w/ key off... should be ~12

then when you start vehicle, v reading should jump up to ~14.5V... if not, brushes on your alternator is worn...