Is that going to be a generator or something? I thought your batteries were charged from the solar panels anyway.
Mine is an off-grid system that charges the batteries first and then a 1kW inverter runs off the batteries. On sunny afternoons there's enough juice from the panels to supply the inverter directly (upto about 450W at the moment). The batteries just provide voltage regulation for gaps in the solar power (the odd passing cloud).
If I need to charge the batteries from the grid (in Winter) I have to manually hook up a battery charger to them. I bought an old 24V "golf cart" type charger for this. It only puts out 75W but it's enough to stop the batteries rotting in the dark months. Needless to say, I can't extract much solar power October thru to March (with almost none in November thru January). Now in May, I'm making about 7% of my total electricity from solar.