We would like to use this battery in desert conditions. What is the performance of the R9VL and UP9VL batteries at 80°C versus one running at 25°C?

From the standpoint of performance hours, or runtime, at 80°C the R9VL and UP9VL batteries will provide the same or slightly more capacity than it would when running at 25°C. However, 80°C is 20°C above the maximum rated operating temperature, which we do not recommend. The result of this elevated operating temperature is the potential leakage of small amounts (generally droplets) of electrolyte and/or permeation of electrolyte solvent through the plastic surfaces of the battery, which will cause reduced performance over time. Extended exposure to elevated temperature can also result in battery swelling, which, depending on the size of the device's battery compartment, may make it difficult to remove the battery.From the standpoint of performance hours, or runtime, at 80°C the R9VL and UP9VL batteries will provide the same or slightly more capacity than it would when running at 25°C. However, 80°C is 20°C above the maximum rated operating temperature, which we do not recommend. The result of this elevated operating temperature is the potential leakage of small amounts (generally droplets) of electrolyte and/or permeation of electrolyte solvent through the plastic surfaces of the battery, which will cause reduced performance over time. Extended exposure to elevated temperature can also result in battery swelling, which, depending on the size of the device's battery compartment, may make it difficult to remove the battery.