# Car battery capacity in colder countries

The capacity of the battery is affected when the temperature drops, particularly Lead-acid batteries. So how in cold countries this situation is solved.

In this PDF about automotive batteries at low temperature, they have mentioned the specific gravity of the electrolyte is affected when the temperature dips proportionaly the charge as well. This also observed from the graph.

And also is there is any possibility, I have load of 2 amps apart from starter will it function when the battery capacity is reduced to certain low percentage(eg. 50%) at the time of temperature drops.

• It is a bit unclear what you mean by "colder" countries; in the really cold ones you solve the problem by letting your car running. Commented Feb 2, 2016 at 10:23

"The capacity of the battery is affected when the temperature drops"

That is incorrect, it is not the capacity (amount of energy stored) that gets lower at lower temperatures. It is the internal resistance of the battery which increases and this lowers the current capability of the lead-acid battery. So you will be able to draw less current (and power) from the battery at low temperatures. The amount of energy stored does not change.

If a lead-acid car battery is in good condition it will still be able to start a car even under cold conditions. A workaround could also be to turn on the lights of the car before starting, now a current will flow warming up the battery and increasing it's current capability. Of course you should only do this when you are sure that the battery has enough stored energy.

• How the capacity of the battery is measured? So that i wont operate my load when the battery is not capable of delivering the power. Commented Feb 2, 2016 at 11:23
• @NaveenRaja The electric charge capacity of a battery is usually measured in Ampere-hours (Ah), and it determines what current you have to draw from a full battery in order to discharge it in one hour. The energy capacity of a battery is measured in Watt-hours and is equal to the electric charge multiplied by the nominal voltage. The nominal voltage of the common car battery is 12V, so a 50Ah car battery would have an energy capacity of 600Wh. How much current you can draw is completely distinct from the capacity, and that value falls with temperature.
– jms
Commented Feb 2, 2016 at 11:49
• to answer your question "how is this solved?". In colder countries there are a lot of roadside assistance companies that help jump-starting cars with aging batteries in cold weather. In other words - it's not solved...
– RJR
Commented Feb 2, 2016 at 11:55
• @RJR so in new car batteries this problem doesnt happend? Commented Feb 2, 2016 at 12:08
• @NaveenRaja correct - in new batteries it isn't a problem (doesn't mean it doesn't happen), but generally a newer battery will have enough charge in even cold weather to start the engine. Once started there's no issue obviously as the alternator will provide power.
– RJR
Commented Feb 2, 2016 at 12:56

So how in cold countries this situation is solved.

It helps to keep the car in a garage, particularly one that is attached to the house.

It helps to install an electric heater to keep the engine warm or to warm it up before attempting to start the car. In cold places, outlets for engine heaters are often installed in front of parking spaces at motels and apartment buildings.

I have occasionally taken the battery out of my car and warmed it with hot water in the kitchen sink.

Many people have a battery charger. I have occasionally assembled a charger by connecting a rectifier to a big variable transformer.

In cold places most people keep jumper cables in their car so that they can get assistance from any willing person who has a running car.

• FakeMoustache said the internal resistance of the battery increases so that current capability decreases. So "Many people have a battery charger. I have occasionally assembled a charger by connecting a rectifier to a big variable transformer" how does connecting a battery charger will solve this problem Commented Feb 3, 2016 at 4:06
• The higher internal resistance lowers the voltage available to crank the engine, but the battery will often crank the engine at a lower speed even though the cold make the engine harder to crank. If the engine doesn't start, the battery will be depleted and ready to take a charge. The charger will restore the charge and the charging current flowing in the internal resistance will warm the battery. Even if a battery is fully charged, it will accept a little current from a "trickle" charger, and that will warm it somewhat.
– user80875
Commented Feb 3, 2016 at 14:36

The standard method of measuring the capacity of a battery is to use a variable load that draw a constant current from the battery. For some small battery and current you can use a regulated power supply in series with battery and connect them to a load, to draw a constant current from the battery.

• how amp-hours method is used to determine the charge of the battery? Commented Feb 2, 2016 at 12:05
• Amp-hours is simply the product of current (Amps) and time (in hours) how long that current can be maintained by the battery. So a 10 Ah (Amp-hour) battery can provide 1 A during 10 hours, or 2 A during 5 hours or 10 A during 1 hour. (In practice, high currents cause more losses so in practice at 10 A the capacity will be less, for example 10 A during 40 minutes instead of 60 minutes). Commented Feb 2, 2016 at 15:00