Plastic is non-conductive, that's why it's used in the casing. Moisture that is not connecting the two poles of the battery and completing the circuit should have 0 effect on battery life. I could see temperature affecting the chemistry inside the battery (and it does actually, that's why batteries have a rating in CCA-cold cranking amps as well as CA-cranking amps), but that's about it. Concrete may affect a battery's life adversley over a long period of time due to it's temperature, but it's not anywhere NEAR the battery killer the old timers would have you believe. I've worked in parts for 7 years now, and I've been around a LOT of batteries, both new and old, on shelves, pallets, and concrete floors. New batteries went bad on the shelf over several months regardless of whether they were on the floor or not.