Quote Originally Posted by 36 sedan View Post
A while back I had the same problem with a newer Optima red top in my sedan. My charger would not charge it no matter what I did. So decided I'd try an Optima charger, claimed it will recover a dead battery that others won't. Sure as heck did and a couple others since, pretty much paid for itself already.
One of the methods Optima suggests is to connect a known good battery in parallel, hook the charger to the good battery and the charger will then sense an acceptable minimum voltage and push the charge. Check to ensure that the dead battery is not getting hot or hissing (off-gassing) after ten or fifteen minutes, and after an hour check the voltage on the dead one. If 10.5V or more, unhook the parallel battery, re-connect the charger to the dead one and let it finish.

Another way is to buy a new charger that has a setting for AGM batteries I tried the cheap route, and it worked!