A battery tender is worthless as a charger, they don't put enough current in to charge a dead battery up. They will charge a slightly discharged battery but they are meant to maintain a battery that doesn't see much use.

Now that you have it at 11.6 volts go buy a charger with an AGM setting and let it charge on a 6-12 amp charge. The optima brand chargers are great, I have the 4 amp smaller one and it does very good despite the low output of 4 amps. Even if your optima doesn't come back an AGM charger is good to have if your purchase another AGM battery regardless of brand.

Most chargers won't kick on if the battery is below 10 volts, that is the reasoning for hooking another battery in parallel. This would apply to any battery not just an optima.