My sailboat is a 1972 Cal T/4 (24í, fiberglass). The boatís electrical system consists of a 12V battery and the electrical consumers (lights, speed & depth and a VHF) there is no charging system installed on the propulsion system which is an 8 hp outboard gas engine. When I bought the boat (four years ago) I replaced the battery with a new Interstate Marine/RV deep cycle battery. At the same time I also bought a Guest (model 2611 three stage) 10 amp battery charger to recharge the battery from the electrical source at the dock.
My electrical usage is extremely limited. When I sail I have the depth sounder on (minimal draw) and the navigation/position lights go on after dark (probably three times a year) thatís about it. This winter I took the battery out and brought it home to store it. I just checked the voltage and the (12V) battery was reading 8.5 volts; it has not been used in months. The last time I had it on the charger was probably August. I just hooked the battery up to the charger and the charger was indicating that it was delivering a 10 amp charge (LED lights on the charger) and I measured 13.8V at the battery. A half an hour later the charger is delivering something less than 10 amps (LED light out) and I am reading 13.4V at the battery. Here is my question; I seem to remember reading recently here on this forum that if a (12V) battery reads less than 10.5 volts it is ďshotĒ and itís useful life is over is that correct? At what point is this slightly used marine battery finished? It is probably the least used 4 year old 12V marine battery on the planet.
Second question; the Guest model 2611 battery charger ownerís manual states that it will not boil off the electrolytes in lead-acid batteries when left unattended. Does anybody leave these battery chargers on all the time when the boat is at the dock? I see lots of power cords going to unattended boats at our marina. I live in the Pacific Northwest (Seattle area) so we seldom get very cold weather. The salt water never freezes and the larger lakes donít freeze either and it is seldom below freezing (32F/0C). What are these power cords powering? Are they running heaters? Or are they powering up the battery charging systems. Iíll ask one of the owners the next time I see them but in the mean time Iím asking you folks.