Well, not having a charger at the time just put it on the shelf in my garage and forgot about it, for two years now. Basically the electrolytes in the water attach themself to the plates, and they choke the battery from being able to re-charge properly... 3 of my 6 cells were sulphated, that is why I couldn't get more than about 5.5v charge to stick (2.2v/cell), it would just drain overnight. You have to "shock it" back to life to turn that sulfate collections to Electrolytes, and allow the plates to except the charge.
So I followed these steps:
- Connect a known good battery (12.6 - 12.8v) to the dead battery in parallel (+ to +, - to -) with jumper cables.
- Connect the charger to the Battery to start charging it.
- Check every hour or so until the dead battery is at least 10.5v (min for an auto charger to recognize it as a good battery)
- Continue to charge the prevously dead battery until the Charger shuts off (or it gets too hot, it can get warm, but not hot).
- Wait 24 hours for the surface charge to dissapate (mine ended up at 14.23v)
- Properly maintain the battery with a solar charger, or maintainer charger.
Well it seemed to work with the Red Top (due to spiral cores of their plates and the very low internal resistance), I'll give this a try with the deep cycle (Marine/RV) that came with the trailer too, maybe I can get some life out of the old girl after all.