I was having the same problem so last year I put a couple of 20 watt solar panels on the cabin top. Now, even after sailing without using the engine for a couple of days I find my batteries fully charged when I return to the boat. It is particularly handy now since I find that really like my electric winches and probably use them too much. I haven't used a winch handle this season except to tension the mizzen as the final stage of raising it. 40 watts of solar panels does a nice job of keeping my 400 amp hour battery bank fully charged