I'm with Doug. First step is find out what charging capabilities your converter has. How the batteries are maintained after charging is important. "Trickle" charging is rapidly being replaced by "Float" charging. Float charging is much more effective and is accomplished with the newer smart chargers, converters, and battery minders (or battery tenders). Basically, float charging gives your battery the current it needs and no more. Trickle charging is a constatnt charge that can give your battery more than it needs, which will shorten its life.
Edit: Battery tenders (float chargers) do not replace battery chargers. They are for after the battery is charged.