I think you'd be best served by installing an upgraded converter/charger. If I understand the nature of battery charging properly and am doing math about right (both of which are questionable assumptions!), you're getting maybe 7-10A charging current out of your current converter/charger...not a whole lot.
The main engine (at idle) might end up being a bit quicker than the existing converter/charger, but it won't be super speedy. The alternator's output is comparatively limited at idle speeds, and some of it is going to power the engine systems like the fuel pump etc., and some more is going to recharge the chassis battery.
