Solar charging multiple batteries

First off how are they charged at the moment?

Buy 3 @ 1W 12V solar panels for under $20 the lot and a few metres of second hand wire.
No regulators or any other messing about required.
Cheers,
Peter
OKA196 motorhome

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Hi Nick, Happy New Year to you.

For purposes of storage you are not looking at keeping the batteries at their "perfect" voltage level. It is merely desirable to keep them at a near full condition. So it is acceptable to simply join them all in parallel and connect to your existing solar panel via its regulator. The interconnection cable need not be large…. 10A rated wire would be adequate, but disconnect it before returning to operational service as it could be damaged by large currents during starting discharges. For safety's sake you may wish to incorporate 10A fuses at each battery connection.
My MB Sprinter has its lead-acid starter battery connected to the auxiliary Lithium battery and both maintained by either the solar panels or a small maintainer mains charger when in storage.

Years ago on my neighbours Mazda BT50 we put a Redarc SBI 12D 100amp battery isolator between the starter battery which was a calcium battery and the aux an agm. With the solar panel attached to the aux when it was charged the isolator would switch over an keep the starter battery topped up that's the basics Redarc have info on their site.
Once it was setup there was nothing else to do no disconnecting things if the vehicle sat for weeks at a time. Just jump in turn the key and go very simple.
Can't see why it won't work on a boat.

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Nick, As the picture progressively unfolds I would suggest the following:

I make the following presumptions……..
*Battery 1, a flooded LA is charged by the engine alternator and provides to the engine and starter.
*Battery 2, A deep cycle LA is charged via the Narva relay and provides to the trolling motor.
*Battery 3, A flooded LA battery provides to the anchor motor.
*The solar is connected to battery 2.
It is highly desirable to retain the Narva relay to ensure that your activities of trolling and anchoring do not deplete the starter and thus being not able to start the boat motor.

So I would suggest that you configure the boat as follows…….
*Leave battery 1, battery 2 and the Narva as they are.
*Connect battery 3 directly in parallel with battery 2 to become essentially a single battery which provides both trolling and anchor needs.
*Leave the Narva connected between battery 1 and battery 2 to priority charge battery 1 and progressively charge batteries 2 & 3.
*Place a switch between battery 1 and battery 2 so that when the solar is alone providing the sustaining charge it will charge all three batteries. This can be just a standard 10A switch as it only has to handle the solar charge current. Turn this switch on when the boat is in a storage condition and turn it off when the boat is in use. If desired, this switching could be automated by using a relay driven from the engine ignition circuit.

In this way the solar, or a mains charger, would maintain the batteries in storage. When sailing, the batteries would all be charged by the boat motor, and the starter battery would be reserved for starting the boat motor.
The small differences in battery specs would be of little consequence.

In storage mode, the Narva may become energised if the solar voltage rose above 13.3 volts and the Narva would then consume about 0.5 Amps from the solar contribution but this is only likely to occur when the batteries become fully charged so is probably of no consequence. It could be managed if necessary.

I believe that these simple changes will provide what you are seeking at little expense.