Why does an Optima battery take a different charger
Yup. Those batteries are CHEMICALLY different than standard lead acid, and should have a lower charging voltage. Ideally, you should actually have a different voltage regulator on the car. I think one of the members here found an aftermarket regulator made for them
Might be this, but I don't actually see an adjustment, and nothing is said about the range of adjustment
http://store.alternatorparts.com/partnoc8313.aspx