Why Won't a Frozen Battery Start a Vehicle.

Do yourself a favor and buy a battery blanket before the battery freezes hard and splits the case.

--
We now return you to our normally scheduled programming.

Michael A. Terrell
Central Florida

I am very not an expert, but I can tell you what I know (or... think I know).

1) The battery is in perfect condition when frozen, unless the ice has destroyed it.

2) When you put a huge load on a cold battery, the voltage will sink. The internal resistance has become very high. My theory is that there is ice crystals at the plates inside the battery, so therefore the 'active surface' is very small, compared to normal conditions.

I recently found a battery with one frozen cell. I took it inside the house and tried to put a load of about 1 A (12 W) on it. The voltage dropped from 12+ to about 3-4 V instantly. As the hours went the battery got less and less cold, and after about 8 hrs, when I connected the load again, the voltage dropped by tenths of a volt.

Where I live, the temperature sometimes goes below -40C, but there is no problem starting the cars. You should check the acid inside the battery (there are meters for that). Also.. it might be the oil and water inside the engine that makes it much much heavier to move around, and therefore the starter + the weak battery can't do it. Try an engine heater ;o)

BR Dennis Olsson

Storage battery output decreases with decreasing temperature. That's why here in the US rated battery peak current capacity is generally cited at 0F. Below that temperature capacity falls off rather quickly, and by the time that the battery temperature reachesst the freezing point of the electrolyte, the battery's output is virtually zip! :-)

For what it's worth, a fully charged battery freezes at a lower temperature than a partially charged battery. Also, if the battery electrolyte does freeze, it will likely split the case and ruin the battery.

If you're dealing with temperatures approaching -30C, the solution is to place an electrically heated thermal blanket around the battery, plus continuouly trickle charge it. At these temperatures, you're also going to need a block heater to warm the engine block, else if it does start the lack of lubrication will destroy it in only a few minites.

Harry C.

You snipped the part where I recommend the battery blanket. I learned this first hand at Ft Greely, Ak. which was he US Army cold weather test site in the early '70s. Nothing would start without a heated dipstick, a battery blanket, and a lower radiator heater hose, if the engine was water cooled. The 90 weight oil in the rear end and manual transmissions was replaced with 30 weight for the colder months, and each vehicle was allocated a separate 20 A 120 VAC circuit for the heaters. It was so cold that some vehicles still had to be towed to a heated garage for a couple hours before they would start, even though all the heaters were in use.

--
We now return you to our normally scheduled programming.

Michael A. Terrell
Central Florida

This graph says it all.....

Capacity at high current is down to 10% of rated capacity at -30.

When I lived in Montana, the temp. would routinely drop to -30F. I kept a spare battery in my kitchen under trickle charge. I would take it out with me and jump start my car and then bring the battery back.

Yes, I had to go out and start the car every 3 hrs or so while at work. I didn't worry about antifreeze as I drove a '66 Corvair.

Al

--
There's never enough time to do it right the first time.......

[...]

A battery is a chemical device. All chemistry happens slower at lower temperatures --- the molecules are moving slower, and they have less energy to overcome potential barriers.

The energy that a battery stores is stored in the bulk electrolyte, but the chemical reaction which extracts that energy only happens on the surface of the plates (where the electrolyte and the electrode come together, naturally). After a particular molecule of battery acid gives up its energy as electricity, it needs to diffuse away from the plate, and a fresh one needs to diffuse in. The speed at which things diffuse is dependent on the temperature. So if the battery is cold and you're drawing a lot of current, you can end up with a thin layer of discharged electrolyte next to the plate, even if most of the battery is charged. If you wait a few moments, the electrolyte will even out, and the battery will appear to recharge itself.

(Disclaimer: I'm not a battery expert, but the above is what I've been told, and it seems to explain the observed behavior of batteries.)

--
      Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1