Battery Performance: as Temperature Drops, Battery Performance Slides

December 12, 2009

One thing that you find interesting as you read blog posts about hybrid cars and battery technology is the amount of information that the average car owner does not have much knowledge when it comes batteries and battery technology.

Indeed, it seems that people seem to take their car batteries for granted they do and are quite surprised when they find their batteries fail during extremely cold weather, especially if they have been in use for more than three years.

Three to four years, in fact, is the average age at which the American Automobile Association recommends that car owners replace the batteries in their vehicles.

There are whole schools of study just devoted to the chemistry of batteries and their reaction to cold and heat, but it seems that as more and more people are purchasing hybrid cars, you would think that more people would take the time to study batteries and battery technology. It would stand to reason.

However, for some reason they do not and when you log onto a hybrid car blog you are likely to find people complaining about huge drops in performance as the temperature drops below freezing.

It's a simple matter, though, to find out some basic information about batteries or battery packs just by looking at the owners manual that comes with your car or the manual that comes with the battery charging system.

For starters, car owners would find out if they were to take the time to read their owners manual that there is a certain range where batteries perform at their peak. It is generally are your ready for this between 68 and 72 degrees Fahrenheit that batteries crank out their maximum power.

The acceptable range of battery performance, of course, is much wider than that so youll also find out that batteries are said to perform best in a range of about 40 to about 80 degrees, or about what you can expect in most areas of the country. This has always been true of the standard lead/acid battery the power cell of choice for the auto industry for more than a century because of its power density/size ratio (you can pack a lot of punch into a small space) and it is true today. Indeed, youll find its also true of the Lithium/ion and Nickel/Metal Hydride batteries used in the 144-volt systems you find in todays hybrid cars. The optimum operating temperature range of the average hybrid car is in the same temperature range. Its a matter of the physics of batteries, something this item wont endeavor to cover because there are many variables and formulas at work to mean much to the average car or hybrid owner, except the information that when it gets cold your batteries wont perform as well.

There is one figure that you should know and that figure, thanks to Wikipedia, is this: the average battery loses power at a rate of about 0.22 volts for every two-degree-drop. This means that for your battery will lose about 1 volt for every five-degree-drop in temperature.

Putting this into perspective, lets say a load test on your battery/charging system reveals that at 68 degrees your battery is putting out about 14 volts. This is just about on the money for a fairly new, fresh battery.

A funny thing happens as a battery ages and it has to do with the chemistry of the battery. Chemists have found that a number of internal side reactions that rob the battery of power occur that you have no knowledge of. The losses may be in the .10 of a volt range but they do add up over time so that by the time a battery approaches three or four years old, it may only be operating at a marginal 13 volts. This is enough to crank your car over and keep it running, but, when the weather starts to get cold and the losses start, you begin to find your 13-volt battery at 30 degrees, is an 11-volt battery around 20 degrees and a 9-volt battery around 10 degrees.

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