Double check the readings and take another SG sample on Battery #1. Either that, or it's been taking the brunt of the charge with the way you have the batteries wired, or which terminals you attached the Mega Watt S35-12 to. Ask folks for proper method of connecting to which terminals, the Mega Watt S35-12... there is a proper way to do it, in the event battery #1 is indeed showing 1.300 for the SG on all three cells.
Also, check the water level on battery 1 compared to the other 3... Is it the same, or a bit lower? If you are in AZ, very, very hot down there. Ask MexicoWanderer about heats effect on electrolyte, and how to get your electrolyte to Tropical Blend or Summer Blend... you might need to run them a bit higher on distilled water to drop the SG a bit, deliberately.