Here is a good trick. When trying to revive a dead battery , connect a good battery in parallel w/the dead battery as you were going to jump start . These two batteries need to be the same . Lead acid , AGM , etc. Now hook your charger to the good known battery and put your charger on high and let charge for about an hour , then set on low and leave for a day or two. When you are finished , load test the battery and see if your battery passes muster. Remember , all connections have to be perfect.