It is possible to save a Big $200 AGM battery with the right know-how!
Remember this will not work on every dead battery, but it might be worth a try. My big expensive two-year-old AGM battery got accidentally unplugged from its maintenance charger. So it sat for over three months connected up to a computer age car and had drained away to where it would not take a charge from any of the battery chargers I had on hand. It would not even show low voltage on my battery tester. Watch as I try to revive it.
