A voltage of 11.6 measured AT THE BATTERY TERMINALS indicateS unequivocally a dead battery!
If such a low voltage is measured ELSEWHERE IN THE CIRCUIT, while the terminal voltage is okay, the indication is a problem IN THE CIRCUIT.
to which you refer will have a decent voltage read-out, but that will not help you if you are not "plugged in"
I take it you are new to seafaring. I make bold therefore to offer you a chart I use in TrentePieds
, which, by my choice, has no fancy electronic doodads.
This chart is used in conjunction with a hydrometer that measures the Specific Gravity of the electrolyte in standard, middle of the road, FLA batteries. A hydrometer that will do the job nicely will set you back the princely sum of twenny bux, and then you have absolute assurance at all times that you will know the actual State of Charge of your batteries. Install your batteries so you have easy access to them so you can "dip" them without having to shift everything in the boat
You should never let your SOC go below 80% if you want reliability
and long life from your batteries. If you observe that rule faithfully, even batteries of middle of the road quality, bought at auto parts
suppliers such as Lordco, Bumper-to-Bumper or NAPA, will last you four or five years. They are, nevertheless consumables! But they are cheap
, so who cares :-)?
You will see that the VOLTAGE difference between fully charged and 80% (the lower tolerance limit) is so little that you are likely to be misled by ordinary voltage meters fitted remotely from the batteries. Go for the Hydrometer and you get the data "straight from the horse's mouth" :-)!
Do yourself a favour and prepare an "energy budget" accounting for all the use of juice you can foresee. Then install enough battery CAPACITY that you can use all your electrical
gizmos according to your "usage habits" for the entire time between charges without drawing your batteries down below 80% SOC.
Remember that the alternator
fitted as standard on your 40 horse Yanmar
just won't cut the mustard! Nor will that fitted as standard on any other 40 horse engine. Make sure to replace it with a machine that can produce, as a minimum, in an hour or two of motoring, all the juice you use in 24 hours. But have regard to the fact that there is a limit to how fast FLA batts can absorb a charge!
Other devices such as solar panels
should be seen "in the same light" so to speak :-) And here in the Salish Sea, part of what is not without reason called "The Wetcoast", your solar panels
will only function at rated output a very small proportion of the time, if ever! And even then, at 49ļLat and even more, the insolation is far less than it is where the coconuts grow!
All the best :-)