Clean and decorrode clamps on battery. Also check current draw for all other components running. If you are running anything that needs elec. the available current for charging battery(s) is substantially reduced. Fridge, AC, furnace, hot water heater, lights, tv, radio, and etc will significantly lower the ability to charge.
2011 Chevy 1500 SB 4x4 5.3L w/trailer tow
2013 Zinger ZT23FB
Reese Weight Dist. w/friction sway control