I did have to clean and replace the battery terminals a year ago or so because they were all corroded and janky. I used the autozone duralast terminals and they seem to be doing real good. Another way I knew my battery was bad was when I hooked up the charger it would only "charge" for about 5 minutes then say the battery was full. The voltage was only 11.8 or something after it "charged" and that is how I knew it was a battery. The voltage should be at 12.5-13v when its fully charged.
And agreed, check your grounds and look at the negative cable right behind the battery. There is a bald spot were the wire connects to a clamp on the wheel well. Make sure the wire is still solid there and of course at the starter.