Why Batteries Drain More Quickly In The Cold Weather

This morning as I was about to leave for work, I mentally crossed my fingers as I turned the key in the ignition. My car's battery is not that old, but with the temperature at 6 degrees and my car being out overnight, I knew even a brand new battery might have a problem. My car started with just a millisecond of hesitation, but the iPod I had left in the car was not so lucky. Even though it was connected to the "always on" power receptacle, it had no charge at all. Those two incidents got me wondering, why does cold weather take such a toll on batteries?

The simplest explanation I could find (and by "simplest" I mean the one I could understand), is that the power, or current, that batteries supply is dependent on chemical reactions and those reactions are slowed by freezing temperatures. Since the reactions are slowed, less energy is produced and the power output is lowered; with a lower output, the battery cannot keep up with the demand and can go dead, producing no current. (Fun fact: battery drain caused by leakage, on the other hand, occurs more slowly at cooler temperatures than at warmer ones). That's a brief explanation on why your car wouldn't start this morning.