Best way to charge batteries when Boondocking?

I like charging my batteries with the 125 amp 4 stage charger in my Magnum. The cable between the charger and the batteries is about 3 ft, and is 0/4 (0000) gauge, sized for the 450 amp surge my inverter can draw starting heavy loads.

One 2000 watt generator will allow it to run at full power around sea level, or about 90 amps at high elevations.

Haven't noticed the length of my AC cord affecting the charge. Sometimes it's a 30 ft 12ga cord, sometimes its a 50 ft 10ga cord