I have a 1996 Cavalier with a 2.2 engine.

For several months now my interior lights, including dash lights, have been flickering. All exterior lights do this as well. Both are very noticeable (to the point where I'm surprised I've yet to be pulled over for it). It also tends to lose power when going up hills, particularly in snow. I was attempting to pull a fairly steep hill covered in snow, but when I pushed the gas pedal all the way down, my power would go in and out almost completely.

I thought it might be the battery cables at first, and cleaned them, but the problem has persisted. So, I took my car to Advance Auto, they did the alternator/starter/battery test and they told me it was a bad battery. My dad is a very seasoned mechanic and said this problem is not likely to be caused by a bad battery, but offered no specifics.

If anyone has further insight into this or other things I should try before spending all that money on a battery, it would be greatly appreciated!