I'm just finishing up putting my new engine and mods on my 07 gt500 and went to load the new tune but I think my motorcraft battery is shot. It's showing the red light and I have had it on a trickle charger for the winter and just re-installed it into the car. So assuming its dead whats a good battery replacement? Go back to OEM? I have had good expereirnce with the Optima batteries and for what the motorcrafts usually run I could probably spend a little more and get the optima. Anyone have an opinion and is anyone running the optima? What size group fits good?