I went to get a battery for my mustang after the original Motorcraft lasted me 11 years. I was going to purchase an Optima, and one of the store employees said "I'm sorry sir, but your charging system on your Ford Mustang is not designed to charge this battery, and is not compatible." I was a little surprised to say the least considering I personally know people who run the Optimas without issue in their Mustangs. Ended up getting a lead acid replacement instead somewhere else.