cold battery acid = poor starting?

[wemorgan]

This afternoon I started my wife's Smart car for the first time in 1 week. But it took at least 6 turns of the key to start it. That's the first time that's ever happened. The weather has been typically cold this past week and was about 3-4 degrees Celsius this afternoon. The engine was turning freely, but just not firing. So it felt like the battery was healthy.

Mechanically-electrically what's happening? Is it just that the acid within the battery had cooled down over the past week? Or was it that the engine block had cooled so much as to inhibit the combustion process?

edit: the reason I ask is that I've read various threads of batteries dying in the cold weather, but I'd expect the starter motor to turn slowly, but the Smart car turned over as usual, minus the ignition.

 

[grober]

Battery output current varies according to the temperature of the electrolyte.
In really cold climates you should switch on the headlights for a few minutes to warm the electrolyte up before trying to impose a large starting current load on the battery. That's assuming your battery is in a good state of charge initially It's important to keep any battery charged in really cold conditions since a discharged battery will freeze more easily. Its possible that the battery output voltage drop which occurs during the starting phase is increased if the battery is very cold may have caused some ignition malfunction but with solid state ignition I would have thought it unlikely.
The reason people have battery problems in cold weather is usually that their battery is on its way out and cold weather just puts its under greater strain. The fact your engine was turning over freely means the battery is probably fine. If the outside air temp was 3-4 C that's not really cold, however the electrolyte might have been considerably colder. In the old days folks used to take their batteries out of the car and inside to the warm overnight to aid cold morning starting in very cold weather but nowadays that's simply not practical since the car's electronics would suffer a nervous breakdown deprived of their "volts" overnight.

 

[wemorgan]

The reason people have battery problems in cold weather is usually that their battery is on its way out and cold weather just puts its under greater strain. The fact your engine was turning over freely means the battery is probably fine. If the outside air temp was 3-4 C that's not really cold, however the electrolyte might have been considerably colder.

Over the past week the temperature in the Midlands had regularly dropped below freezing each evening. So I could well imagine that the electrolyte could have been colder than the ambient temperature.

 

[Ted]

Battery electrolyte has a negative temperature coefficient. Thay means that its resistance goes UP (and is therefore less efficient) as the temperature goes DOWN.

You battery is also likely to be less than fully charged - lights, heater, rear demist etc at this time of year.

Add the fact that engine oil is thicker as the temperature goes down, and this is the time when the battery (and charging system)is most stretched and most likely to give problems.

Any of the above being less than perfect, and you are likely to have issues which would not happen at any other time of the year.

 

[wemorgan]

I'll get out the multi meter tomorrow and test the voltage. I tested the other car yesterday and it was 12.4v (engine off). The Smart car does suffer from quite a few short jouneys I admit.

 

[lynall]

Wifes car not started for approx 2 weeks fired up instantly as normal.

I reckon as said battery duff or soon will be, buy a new one for peace of mind.


Lynall