As far as bringing back a battery is concerned, it has always been my understanding that a looong charge time with low amperage is the way to go, followed by cycling the battery, (repeated charging and discharging).
This guy seems to agree (be careful, his manner is a bit over the top but I think he gets the message across);
https://www.youtube.com/watch?v=6x-J...ndex=23&t=523s