I saw the post from 8gy....
"The charged it overnight with no luck"
I did the same for 2 nights w/o luck, just seemed totally DEAD ! Only 8v.
Last night just for chuckles, I threw the battery on the charger.
This morning I checked the voltage and now have a strong 13v
Going to check the voltage in the morning to see if it is holding.
No idea what was going on with my first charging attempts, could be the charger itself, but now seems like the battery is back from the dead !
FYI the battery is a 'sealed' battery and never requires water.