If that battery can't start a 30B3, even if it were at 11.9V, it is toast.....
Excellent point !!! This point can not be emphasized enough!!You don't want to top off your batteries in the winter with water unless you are going to do a charge that will create a bubbling of the batt. acid. to mix it. Otherwise the water can freeze on the top.
I like to see all flooded batteries charged to "full" (14.6V - 14.8V to at least 1% of capacity in accepted charge current) then equalized before winter.If the batts are fully charged in the fall and are disconnected, there will be no discharge. As Main Sail has drilled thru or heads now for many years.
The battery is only a year old, and was topped off before winter storage (indoor heated), and ALL the batteries were disconnected from everything.