What is the outer metal casing of an alkaline battery made of?
After you measure the steel case Temp also measure the ESR or incremental voltage drop for rise in I and then compute Pd from Pd= I² * ESR and not simply V * I...  

ESR will be a better indicator of heat loss, Pd and thus   the linear temp rise for Pd as V drops and I rises . 

Then compute the thermal resistance Rth_ca, Pcase is an indication of the internal Anode temp which is hotter.  Thus ESR vs Tcase and then Rth_ca=ΔT/Pd (steady-state) (thermal case to ambient resistance.)    Moving air, ice, removing plastic and adding enclosure will each affect this thermal resistance and temp rise .

Hotter batteries also have lower ESR and more power available YET age much faster. (50% life reduction every 10'C rise regardless * mAh consumed)

The same is true for LiPo cells and Lead Acid although LiPo's can have a thermal runaway effect above ~200'C? core temp and explode.