Can I add a solar 12 v. charger to optima battery?

Make sure you have a fuse in series right at the connection to the battery. Yes it will be fine. It won't recharge a discharged battery but it may help to maintain the battery at a useful charge level.

 

Was just using one on my dying OEM battery to keep it charged while I was at work. It seemed to work fine except for the lack of sun this time of year.

 

I think the solar charger might help a dying battery make it through the sunny summer, but if you're having battery problems in the fall or winter I'd replace it because getting stranded in freezing weather is a thousand times worse than getting stranded in the summer.
and ditto about not having any sun this time of year. I wish someone would make some solar fans to fit into those useless tiny triangle windows up front. because summer is plenty hot and plenty of sun so it would make more sense to run some sort of summer accessory on solar power.