I think I need a new battery for my diesel. This morning the starter turned very slow in the Michigan winter. I then hooked up an automatic trickle charger and it says the battery is fully charged. Very strange but I had this happen on a tractor battery as well.. Some how a dead battery still measures 12 plus n=volts but has no capacity.

What is the best battery I can buy? The sources I have here are Wal-Mart, K-Mart, Autozone, Advanced Auto parts. I think there is a small shop that sells Interstate but I am not sure.

TIA.