Re: Voltage puzzle
The no-load voltage may well be 12.9, but it's unlikely the battery is recharged in terms of stored amp hours... put a few lights on and I'd not be surprised to see the volts drop quickly.
btw how did you determine the '60%' drawdown?
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)