What does the internal temperature of a location case do to battery life?

It is usually the dominant factor, and it is under-modelled. A signalling location case is a sealed metal enclosure in the sun; internal temperatures well above ambient are normal. VRLA life expectancy falls roughly 50% for every 10 °C sustained above 20 °C, so a 10-year design-life battery in a 40 °C location case is a 2.5-year battery, and the capacity lost to heat cannot be recovered. Note that AS 7720 addresses internal temperature control and ventilation for signalling equipment enclosures for exactly this reason. Measure the case temperature in February before specifying the battery.