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by Dan Veaner
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Friday, 24 March 2006 |
 Dr. Digit 'Splains It All
I got one of those indoor-outdoor thermometers that communicates with a sensor that is placed outside. They both run on batteries, and communicate by radio waves. I thought this was a pretty good arrangement. I could put the main unit on my desk somewhere and not have cords dangling from it. I could hang the sensor on a tree in the yard and wouldn't need a long wire to make it tell my desk unit how cold it is outside.
In one part of the manual it says to put two AAA alkaline batteries in the outside sensor. So I did. I got everything working, then went back to reading the manual for pleasure. (You see, it doesn't take much to please me...) Whoops! I found a warning not to use alkaline batteries in sub-freezing temperatures, because they freeze. It said not to worry, though, because when the weather warmed up the batteries would unfreeze and start working gain. They suggested lithium batteries for cold climes, because they don't freeze until you get to -40 degrees Fahrenheit.
Swell. I live in New York State. It gets cold here. I want to know the temperature as much when it is below freezing as I do when it is balmy. I'm not so far north that I have to worry about -40 degree weather, though. So off I went to the store to find lithium batteries.
That got me to thinking about how batteries work. As far as I was concerned there were only three important facts about batteries:
1. If you have kids you are always out of batteries.
2. Just about everything needs them.
3. They cost too much.
Here are some more facts. Electricity in a circuit is a bunch of electrons dancing along a wire. They flow from a power source such as a battery along the wire to a device that uses them to create light, show Gilligan's Island or make toast. Batteries have two terminals: positive and negative. When a battery is part of a completed circuit, meaning that a wire goes from the negative terminal to a device and then back to the positive terminal, a chemical reaction takes place within the battery that produces the electrons. They go out the negative terminal, around the circuit, and come back to the positive terminal.
When a battery is disconnected the chemical reaction doesn't take place. That's why you can keep a box of batteries on a shelf for a long time without losing their capacity to make your flashlight work. Of course that assumes that you don't have ravenous kids, powering everything in site. In that case, who needs shelf life?!
Batteries come in all sizes and shapes, with different elements creating that chemical reaction. Cheapo batteries are zinc-carbon. The longer lasting ones that bunny wants you to buy are alkaline. The ones I needed for my thermometer are lithium -- they are more expensive, of course. Lithium batteries are also commonly used in cameras. Cylindrical batteries that so many devices use come in sizes from AAA (small) to D (big). Whichever size your device needs, you always have the other sizes in your drawer, but not THAT size.
In most cases the temperature range of a battery doesn't matter, since most devices are used in and around rooms that are well within the acceptable range. But sometimes you do need to know more about your batteries than you really thought you wanted to, especially if you want to know how cold it is outside.
You can even make a battery with salt water. But I don't recommend it. After all, that would be a salt and battery.
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