" let the very good controllers do their job of keeping the batteries topped up for free. "
A battset in good condition will self discharge 1/2 percent per day.
On a 1000 amp house battset or about 5 amps at 12v DC per day .
Creating 10A of 12v to charge the battery for an hour pr
day would be 120watts .
The savings of not paying for dock power at even 25c a KW, a dollar a month, might easily be overlooked as cheap insurance should the boat need her bilge pumps.