Our Palm Springs Summers beat your Texas Summers
I've consistently got 6+ years out of my batteries. The first was a '87 300E and the most recent was a '95 E420. I was amazed to find the battery on the 420 was almost 7 years old. Of course both of these batteries were 84 month types. My cars have always been garaged but when I come back after a run in 115F temps, I pop the hood and let all of that heat out of the engine compartment. Of course that is not much help on the 420 because the battery is in the trunk but it certainly can't hurt the rest of the engine components.
Anziani
'93 300CE 180K
'95 E420 117K