Why does cold weather kill a weak car battery?

[Fred Derf Veteran]

When I went to start my car earlier this morning (technically yesterday morning) it was completely dead. The temperature was -25C with the wind chill. I did not leave the lights on or anything running off the battery but the car is older now. I don't have a block heater like they use out west and it was outside (rather than inside a garage).

Why do car batteries always seem to die on the coldest nights of the year? Why not on a regular day?

Incidentally someone lent me a trickle charger and I left that plugged in for about 7 hours. After that, it started perfectly (I knew I was in business when I opened the car door and the light went on). Still, even though I'm happy the car works again, the temperature mystery remains...

[Napalm Frog]

I think it boils down to simple chemistry. The reaction in a battery are entirely chemically based. Colder temperatures naturally act as an inhibitor, thus slowing down the internal reactions. The end result is a reduction in electrons flowing in a circuit. With not enough electrons moving per unit of time, there is not enough charge to power something like a car for long enough.

That was a rough explanation, hopefully someone can maybe add a bit more scientific detail.

[brandnewfantx]

I had to replace my battery like early January when it was 29F-33F..

I bet it something fault in aged batteries.

[chconline Veteran]

It's harder to make a reduction/oxidation chemical reaction in the battery happen at a low temperature to create a potential difference. Temperature is directly related to the rate of reaction in most chemical reactions, and since a battery is utilizing simple reduction/oxidation reactions to to make electrons flow through the external circuit, lowering the temperature reduces the amount of electrons flowing from the anode to the cathode. In a weak battery, it only makes things worse... Well, that's my guess anyway, not really into chemistry haha. :p

Edit: Someone beat me to it haha.

[MR_Candyman]

technically, your battery will still work fine in summer, just won't be good enough in winter. I have a deal with my local partsource where if my battery dies for any reason in 5 years I get a free one, if it dies in 7, I get a big discount on the next. This is different than their normal warranty though, but I still like dealing with their normal policy anyways

[Guest]

It's all stuff related to the boltzmann factor.

[John S. Veteran]

Fred I can't quote the internal specifics as some have, but I grew up hanging out at my uncles garage. :) You're going to need a battery soon. A weak cell in a battery can prevent it from starting in cold weather since that's when the most strain is put on your battery. It's not killing it, it's just already weak and you're not needing as much power when the temps are warmer. I noticed mine lagging a bit at the first of winter, and replaced it with the larger option for my truck (1000 cold cranking amps) and it fires up with the same intensity hot or cold.

[Fred Derf Veteran]

What I ended up doing is charging it with a "trickle charger" (as it was described to me). Basically I attached one red clamp to the battery's + and the black clamp to the frame and then plugged this trickle charger in to a standard outlet for about 7 hours. After that the car started no problem. I have heard that it probably will not last which makes me a bit worried that I will get stuck somewhere, sometime in the future.

There was a time several months ago (maybe even more than a year ago, I forget) that I left my lights on for several hours. Perhaps that was what set me on this path.

[h4ck3r4life]

neh not really about the lights.. the alternator would of charged the battery back up in a few minutes....... that temp would of been 13degrees of F --(i dont know how to spell the worlds 2nd longest word)

and the fact that the battery might be 5-6 years old?....I would get one wiht a lot of COLD cranking amps or cca the amps that are written the biggest are usually warm amps look for a sticker that displays cold cranking amps.........I am very sorry if im rambling

go to a autozone or advance auto parts or a local retain chain.. they have a thing now where then can test to see if you need a new battery or not( an amps test??)

[Vettetech]

Looks like its time for the expert to step in. I have been a mechanic for 18 years. I am currently a GM Certified Master Technician and an ASE Master Technician. The reason a weak battery gets killed in the cold is easy to explain. If you read the tag on a battery there are CA's and CCA's. CA means cranking amps. CCA means cold cranking amps. A battery looses 50% of its CA below 32 degrees F. So take a battery that has a CA rating of 600. Then the CCA is around 300. Now if that battery is weak and only putting out 400 CA then that means when temps are bellow 32 degrees that battery will only have 200 CA. That is not enough amperage to turn over your average car or truck. Understand everyone. :yes:

[abecedarian paradoxious]

And Vettetech didn't mention that placing the battery on the charger for 7 hours did two things:

1) it reversed the chemical reaction that depleats the battery's 6 cells' ability to provide voltage- it charged them and resulted in the battery being able to supply enough amperage and voltage to start the vehicle

2) it warmed the battery. This, in and of itself, could've been enough to start the vehicle- if the battery were kept warmer than 0C/32F.

Fred-

a block warmer would not have prevented the problem from occuring. It would have only kept the engine block from freezing. This does two things: makes it easier to crank the engine over due to reduced friction from having a warmer engine; keeps the engine block from being damaged by frozen coolant. Frozen coolant can cause the engine block to crack since water expands when it freezes. You would have had to have a battery warmer to keep the battery in a state to deliver the required power to start the engine or would have had a relatively new battery rated for the ambient temperatures you are experiencing.

Vettetech is correct in his description of battery ratings: cranking amps, cold cranking amps, etc. But they are in no way definitive regarding battery performance since batteries deteriorate with age... some more quickly than others and different battery chemistries react differently to cold weather regardless of the "CCA" rating.

[MR_Candyman]

some battery chargers have a mode that does a pretty good job of restoring a deteriorating battery. I'm not sure how it works but it does. Did it a ew weeks ago to my girl's battery and she hasn't had a problem since.

I installed a battery warmer on both our cars because it does make a huge difference

[Quickstrike]

I have never had a problem.

It was -30 to -40 Celsius everyday in Calgary a couple of weeks back and my car started right up with no problems.

Not garaged or plugged into a block heater.

It didn't sound very good for the first 5 minutes or so though because I would imagine the oil was pretty viscous at that temp.

I drive a '99 BMW 328is. The battery is in the trunk, maybe that helps a little.

[chconline Veteran]

I have never had a problem.

It was -30 to -40 Celsius everyday in Calgary a couple of weeks back and my car started right up with no problems.

Not garaged or plugged into a block heater.

It didn't sound very good for the first 5 minutes or so though because I would imagine the oil was pretty viscous at that temp.

I drive a '99 BMW 328is. The battery is in the trunk, maybe that helps a little.

It was -40 with windchill :p The battery in your car isn't really affected by that.

Either way, my car started with no issues (My 07 Civic). Either way, my parents reported no issues with their 03 Honda Odyssey either.