http://www.tecmate.com/u_optimate_5.php

They are used by the 2-meter radio folks and lots of motorcycle people. Aircraft Spruce sells them to airplane people.

Seems like a highly versatile compact, durable charger/maintainer/diagnostic tool at a decent price.

Perhaps overkill for our needs?

They also manufacture a nice universal USP power cord that you can use to charge/operate your cell phone directly from the ship's batteries should you ever find yourself landed out with a dying cell phone.