I'd try to get shade over the battery box if possible for batteries in really hot environment. It is the combination of ambient temp, direct sun on the box and large charging amps that I see generate the most heat on my set up. I try to mitigate one or more of those. You can also compute the proper charging and floating voltage from the battery specs at given temps and see if you are over.
It seems like different batteries have very different temp specs. Certainly batteries relying on starting battery components are designed to handle really high under hood temps, but also often see pretty incomplete charging in that environment. They get a big initial blast from the alternator but then charging often falls way off before they are full.
Jim
