The temperature was a balmy -19F at the 2planka abode this morning northwest of Boston. To my delight the five year old battery worked and my car started. This summer, on a day when the ole mercury boiled at 96F, the (two year old) battery in my other car decided to end it all. Which extreme is tougher on a car battery?
It seems that sound travels further in colder weather… I noticed this when an airplane flew overhead last night and I swear I could hear the pilots talking. Well, not exactly, but the wind and engine sounds were quite clear. I assume it has something to do with the density of the air at certain temps.
Can any of you scientific types enlighten this liberal arts major?
It’s gotta be the cold weather. You don’t generally see people begging for jump starts in July. There are multiple things going on in cold weather that make it hard slogging for a battery. The first is that chemical reactions just don’t take place very fast at low temperatures. So the battery is going to put out less juice. Meanwhile, the oil in the crankcase has thickened overnight, making it harder to crank the engine. Not to mention that you tend to drive less in cold weather and you’re running a bunch of accessories when you do drive, so the battery probably isn’t at its peak charge.
Also, in the winter you’re more likely to being using accessories like lights, which work off the battery, and more likely to leave them on (at least in the old days, before alarms and buzzes for “lights on” were common). Ditto for all the other cold weather battery/engine problems noted.
And yes, the air IS denser in winter. This will, to some extent, improve sound conduction. Another factor is that in extreme cold ambient noise are often fewer - fewer folks out walking around yakking, fewer animals making noises, etc. So what sounds there are stand out more.
I once read on a webpage (that I have since been unable to find) that during the summer, heat rises from the surface of the earth and deflects the sound waves as is rises. I don’t know if the air actaully caries the sound waves, or if the temperature gradient bends the sound waves upwards, but it would explain things. Again, no cite on any of that.
At a colder temperature, the athmosphere holds less water vapour - 60% humidity at -10c has far less water than 60% at +30c. I presume this allows sound waves to travel with greater clarity.
Yes, when the engine is running the alternator or generator should be producing electricity to power the accessories and recharge the battery. But there are three flies in the ointment:
Electrical output depends on engine RPM.
Imagine you’re driving with headlights on, heater on with fan set to MAX, electric rear window defroster on, front and rear wipers going to clear the snow. If you’ve got a real fancy car, then the electric seats are on HIGH, the electric mirror defoggers are on, and so are the headlight wipers.
All that consumes a LOT of electricity. While driving at high speed (high engine RPM actually) your alternator can handle all that and still make enough extra electricity to recharge the battery.
But what if you’re stuck in traffic or driving slowly because of the lousy conditions? Answer: the alternator is putting out less than the accessories are consuming and you’re still pulling some power from the battery. The alternator is shouldering some (a lot? a little?) of the load and the battery is making up the shortfall.
2) Recharging the battery isn’t instantaneous.
Even without all the heavy-use accessories, it takes time to put as much electricity back into the battery as was consumed in starting.
In warm weather with an easy start, it may take 10 minutes of normal driving to restore the battery to the pre-start level of charge. In cold weather with thick oil and maybe a bunch of cranking, a LOT more electricity is consumed starting the car and so it might take 30 minutes of normal driving to get the battery back to where it was before the start.
So a day of short hops from stop to stop to stop can easily end up as a net drain on the battery.
Cold batteries hold less electricty than warm ones. So you’re beginning this whole process much closer to the not-enough-juice-to-start-the-car level.
Bottom line: Cold is a triple whammy against car batteries. And the three together are worse than the sum of the three individually. They reinforce each other to make the problem worse.