Alright, my (brand new) battery reads 12.4 when the car is shut off but when it's running it reads an 11.4 and the dash gauge is reading just above the redline. The alternator has less than 10,000 kms on it so I really don't think that's the probelm (I can't seem to get a multimeter reading off the alternator). Oh and when I switch back to the old battery I have the same issue. I recently used a wire brush on the battery cables to clean them up, and that brought the gauge reading to a healthy level and the lights were bright again but now it's back to doing the same old problem. Electronics aren't my strongsuit so I am totally confused by all of this. Any ideas as to what's going on??

 

You checked the connections to the battery, that's the first step. The second step is to disconnect them, follow the battery cables to the other end, remove them and clean them just as well. Ground connections, especially, cause more electrical problems in cars than any other issue.

While you have the other end of the cables removed, check for corrosion under the connectors, wire brush any rust, and make sure any metal-metal contact points are nice and shiny.

Best of luck!