Originally Posted by mitiempo
Most shorepower chargers are sized to get a battery fully charged in a reasonable time. If the battery is down much a maintainer at about 1 1/2 amps would take days to full charge a battery. Engine charging is quick to about 80 or 85% state of charge but the last 15 or 20% will take 8 or more hours regardless of alternator size. Fully charged batteries have a much longer life than batteries left partially discharged.
A maintainer is good for keeping a fully charged battery at full charge over a long period of time which is all it was designed to do.
This is what I have. Unlike a float charger it is capable of bulk charging too. Since it charges at a slower rate, the battery stays cool, ultimately prolonging my batteries life:
Battery Tender® Junior 12V @ 0.75A - Batterytender.com
It does a good job, and since the only thing that I run off the battery is my depth finder and running lights (cabin lights are LED and use their own batteries), I don't use too much battery. Especially since all my sailing is done in the day time. After a long day of sailing I am down to 90-95%. Now that I have a new motor that charges the battery as well I should be in good standing.
I am adding a stereo this year. That may push me into purchasing a larger battery charger.