Hi guys, its been a while...
I left my boat covered and under a metal building for about 8 months between late last year, and up until last week. I have property in other states that I have been working on visiting.
I made the mistake of not having the boat plugged in the entire time. I came back to completely dead batteries of course. So dead, that one of my chargers would not even recognize the battery being connected. All 4 batteries were down to .5 Volts.
I used a different charger, and charged them all back up, and then put them back on the onboard charger (Dual Pro 4 bank) and got them all charged up on there, and I have left it that way.
What do you think the odds are that the batteries are degraded enough to only last half the time or so out on the water? I could typically get a day and and some change on a full charge. These batteries are 3 Decka 27s, and an Interstate DC cranking 31.