Zen and the Art of Battery Maintenance, Part One of Two
(with apologies to Robert M. Pirsig)
Hello, friends, and welcome to the show. You asked for it, so here's your article on batteries (ask and it shall be given unto you...). We'll be discussing both rechargeable and throwaway batteries, so this really is two, two, two articles in one.
One thing before we start - please use the information you will learn here only for the powers of good, and not in some misguided attempt to rule the galaxy. Thank you.
All of us use batteries of many sorts to power the equipment and tools that are a necessary part of our job. And all of us spend certain amounts of money purchasing and maintaining these batteries - sometimes tens of thousands of dollars in a large department. If a battery fails, it might merely be annoying, or could be life threatening. If the battery in your camcorder goes dead while you're taping your kid's first steps, you'll be annoyed. But if a battery fails in your flashlight while you're searching out some punk in a dark warehouse, the consequences could be much worse. In this article, we'll discuss the various types of batteries available, some pros and cons of each, how to choose the proper battery in the beginning, and how to get the most life out of it once you own it. We'll learn about some hot new batteries that might (or might not...) be the cure for all our battery ills. And in the fashion you've come to expect, we'll also climb onto our famous "care and feeding" soapbox.
Judging from the huge stack of notes I've been making over the last several months for this article, we will have to spread it out over several issues. This may turn out to be the mother of all articles... You have been warned. Don't forget to save this part 1 so you'll have it when part 2 arrives in the next issue.
Batteries come in two basic types: throwaway and rechargeables (primary and secondary, to use the official terminology). Throwaway batteries are meant to be used once, then discarded. Rechargeable batteries can be used, recharged, and used again. Each has its place. In some applications either type can be used, but for most uses one or the other clearly will be the best choice.
We need to keep two things in mind when we select batteries. One is the cost of the batteries (both initial and long term), and the other is the reliability. The order of priority for these depends on whether you are a beancounter or the end user of the batteries.
While I'm thinking of it, let's define some basic terms. A "battery" is a device which converts chemical energy into electrical energy. But, to be really precise (yeah, right), we really are referring to a "cell" when we mean a single unit. A "D" sized flashlight "battery" is really a D cell. Several cells tied together makes a battery. A 9 volt "battery" really is that, because it has a number of cells inside. A car battery has several cells. But a penlight "battery" really is a cell. More on this later. I will use both terms more or less interchangeably, unless we are talking technical and I need to use the proper term to be precise.
There are dozens of types of throwaway batteries. Many are exotic, special purpose batteries and we won't cover them here. The ones we will discuss are the popular carbon-zinc and alkaline, and the relatively new lithiums.
The carbon-zinc batteries are the ones most of us grew up on. Remember the old silver Eveready Nine Lives? Some of my earliest memories are of Christmas gifts which used these things, and the 2 cell flashlight our parents kept in the glove compartment. As a kid, occasionally we would use batteries for barter material, together with arrowheads, marbles and other valuable stuff. Those batteries are still around in the same basic design. About the only advantages of carbon-zinc are that they're cheap and lightweight. For very uncritical uses, carbon-zinc are a good choice. They have an average storage life, average power and the lowest initial cost, but probably the highest long term cost. I can't remember the last time I bought any of these batteries. Radio Shack gives them away free in their "Battery of the Month" club.
Regarding the cheap batteries, the most practical use I can see is maybe for kid's toys. If the toy is going to break anyway, or the kid will leave it on all night, why feed the toy expensive batteries? The cheapest ones you can get may last longer than the kid's attention, or longer than the toy itself.
A much better value in throwaway batteries are the alkalines. Duracell and Eveready Energizers are the most popular, and I'd probably use more Evereadys if it weren't for that damned bunny. Radio Shack alkalines are not bad either. Alkalines cost more, but give much longer service than carbon-zinc. Alkalines are three times the price, but typically last five to ten times as long, so you can see which is the better value. (I am using the 1993 Radio Shack catalog as a reference for price, and notes from my own files for technical information).
For most throwaway battery applications, alkalines are the best choice. They're ideal for most flashlights that are not used on a daily basis, for consumer electronics such as microcassette recorders, and for most surveillance electronics. They really are reliable, cost effective, powerful and have an excellent shelf life.
Alkaline batteries first started appearing in the consumer market back in the early 1970's. Since then they have grown to become probably the most popular type of battery. Some advantages of the alkalines over the cheaper carbon-zinc are: shelf life measured in years, good performer at low temperatures, very leakage resistant, up to 10 times the life, do not need a rest period to recover between uses, capable of high current, physically they are very rugged, and by design they are intrinsically safe. A few of the downsides are higher initial cost, and they're heavier (did you think you were going to get all the advantages for free?).
Alkaline batteries are best when used at temperatures of 0 to 130 F (or -20 to 54 C). At lower temperatures than these, the chemical activity slows down significantly, reducing performance. At higher temperatures the chemical activity speeds up, shortening the life.
While we're talking about alkaline batteries, there's one important point to note. In the older carbon-zinc cells, the top of the cell was positive, and the case and bottom was the negative terminal. With the alkalines, the top and entire case is the positive terminal, and the bottom is negative. Many pieces of equipment that are powered by batteries use metal battery holders. Much of the time these metal battery holders are bolted or riveted to the metal chassis of the equipment, which means that the holders are at equipment ground (negative) potential. When you insert alkaline cells into these holders where the case is positive, you will short out the batteries, (the case of the battery being positive, touching the metal battery holder which is grounded to the negative side of the equipment). At a minimum this will overheat and kill your batteries. Worst case is the thing could catch on fire. Since the alkaline cells are capable of high current, a fresh set of them very likely could heat up enough if shorted to cause serious damage. Fuses can't help, because the short is happening right at the battery holder, before the fuse is even in the circuit.
We saw this once in a Mason telephone analyzer sent to us for repair. The customer complained that every time he put batteries in the unit, they would go dead very quickly. What an understatement! Fresh batteries got so hot that you could smell the paint burning. The problem was as I mentioned above - the battery holders were riveted to the metal chassis of the equipment, but the newer alkaline cells' cases were positive. This was not the fault of the Mason equipment, nor of the batteries. We fixed the problem by putting two layers of heatshrink over the metal springs that clamped around the cells to hold them in place. This served as an insulator and solved the problem.
Many pieces of equipment that use batteries have cardboard tubes to hold the batteries. You put the batteries in the tubes and then insert the whole thing into the holder. The cardboard tube is not there to look pretty or because of some obscure Japanese engineering detail. It's there to insulate the positive case of alkaline batteries from the negative polarity of the holder. The manufacturer doesn't have any way of knowing whether you'll use alkalines or not, so he gives you the cardboard tubes just in case.
If your battery powered equipment has those cardboard tubes, use them. If you lose them, fold a piece of cardboard around the batteries before you insert them into the holders, or cut some strips and put them between the cells and the fingers of the holder. I use the cardboard from the back of a pad of paper. The only metal that should touch alkaline batteries is the terminals at the top and bottom. Note: sometimes you can ignore this and get away with it for a while. The paint on the batteries will act as an insulator for a while, preventing the shorting and overheating. Then, likely when you're transporting the equipment, vibration will cause the holders to scratch through the paint on the battery's case, starting the problems mentioned above.
Properly engineered modern equipment will use holders that electrically are not connected to equipment ground (you will see plastic insulators on the rivets on the bottom of the holder). There also are plastic holders or other styles designed for alkalines that will not be a problem. Don't take chances: if you use alkaline batteries, make sure this won't happen to you.
In an earlier paragraph, I mentioned a "rest period" between uses. With the inexpensive carbon-zinc batteries, they need a rest period after a significant drain to recover. Remember our flashlights as kids? You could read under the covers until the light got too dim to use. The next morning the flashlight would be working fine. That characteristic is found only with the carbon-zinc. Alkaline cells don't do this. Once they are discharged and performance starts to suffer, that's it. There's no significant recovery. Cells "recover" because chemicals redistribute inside the cell and start behaving themselves all over again.
Another thing we mentioned about alkalines is their ability to deliver high current. The internal "impedance" (resistance) of the battery determines the maximum current it can deliver. Carbon-zinc cells have a relatively high internal impedance, limiting the maximum current. Alkalines and some other types of cells have quite low internal impedances, allowing for a higher maximum current draw. Remember the "photoflash" batteries when we were kids? They were special types of carbon-zinc cells that were designed to have a lower internal impedance than regular cells, letting them kick out the extra burst of current to fire a flashbulb. I don't think I ever used them for camera flashes, but I do remember the model rocket launchers recommending photoflash batteries for launcher power. This is because the quick burst of current was needed to fire the rocket igniter. For every benefit there is a price. The photoflash batteries were designed to put out a quick burst of current only for a very brief period of time (I say "were" because I don't think photoflash batteries are on the market anymore). Regular batteries are designed to put out average amounts of power for longer periods of time (like in a flashlight).
Carbon-zinc batteries can be recharged to a certain extent, but not enough to increase their reliable life any significant amount. I remember as a kid my father made me a battery charger. Even then I must have had an entrepreneurial spirit, because I charged neighborhood kids a nickel to charge their batteries overnight. It's harmless to try a cheap charger to get a bit more life out of tired carbon-zinc batteries. I doubt that you'll see much more life, but for a kid's toy it's worth a try, and it makes you feel good.
Regular alkaline batteries designed to be disposable cannot be (re)charged. The chemical action in a worn out cell cannot be reversed by charging. In fact, to try to do so will cause a significant heat buildup inside the cell. This heat will cause a buildup of pressure which will open up a sealed safety vent. Once the vent opens, that's the beginning of the end for the cell anyway, because the vent does not reseal and the cell will dry out quickly.
Drawing too much current from an alkaline cell (whether from a short, an accident or poor design of the equipment running off the batteries) also will cause overheating and subsequent quick failure of the battery. "Too much current" is defined as more than 75% of the cell's rated current at 32 F. More information on this as well as current ratings for the various batteries will be given in part 2 of this article.
An interesting type of throwaway battery has finally made its way to the consumer market. Many years ago we read about a battery that could be stored indefinitely, without any loss of power. Ordinary batteries have some sort of shelf life, meaning the length of time they can be stored and still have some power remaining. Shelf lives of batteries can range from days to years. You might wonder what good batteries are that have a shelf life of only a few days. There is a battery called Yardney (the manufacturer) silver cells. They are extremely expensive batteries, but they offer a very high power to weight ratio. My exposure to them was on a military contract, where these batteries were used to power electronic systems in various types of missiles. They need to be on standby for months but be ready to go fairly quickly. Of course, once launched, the missile's life is measured in minutes or sometimes only seconds, and you don't care how long the batteries last. Yardney silver cells were designed to be liquid filled. They would be in the missile dry, in which state they could be stored indefinitely. When the missile was prepped for imminent launch (this is not a drill...), a gas generating squib (small explosive charge) was detonated to pressurize a container of electrolyte. This would then fill the batteries and activate them. Once the batteries were filled the clock started ticking on their life. If the missile wasn't launched, the Yardney silver cells had to be replaced.
Children, don't try this at home.
Anyway, back to the new battery. Batteries stored dry can last a very long time (car batteries usually are shipped and stored dry, and filled only when they are sold). Dry batteries also are safer to ship and store. There is a battery (cell, actually) available now in specialty catalogs that resembles a D cell. The liquid part of the chemicals is stored inside the battery in a glass vial. The battery can be stored virtually forever. When you need to use it, you twist the top of the battery, breaking the vial, releasing the liquid and activating the cell. The idea is infinite shelf life and immediate availability of power when needed. The batteries would have a place in survival kits, fallout shelters and other emergency preparedness stockpiles.
The idea seems valid. These batteries were announced at least ten years ago, but I've only noticed them in the catalogs for a year or so. They're expensive. I believe once activated they have a working lifetime greater than a carbon-zinc but less than an alkaline. Save your money, though, because I think a much better solution to the same problem is (envelope, please)...
The Lithium Battery! Lithium batteries are one of the miracles of modern technology. They have made many electronics products practical for the first time. Lithiums have many, many advantages for all sorts of uses in law enforcement, medical, industrial, security and many other applications. They are relatively recent, a potent addition to the engineer's bag of tricks, and here to stay. Absorb this information well, because lithium batteries will become more and more of a reckoning force in the near future. They also will give us greatly increased performance for much of the electronics we use in our profession.
Lithium batteries offer a very high power to weight ratio (up to five times that of other batteries, and at least twice that of alkalines). They are lightweight, reasonably priced considering their performance, contain no chemicals dangerous to the environment (the politically correct attitude to have, but frankly I don't give a damn about whales...), have an almost infinite shelf life, and offer excellent performance at low temperatures. Hold on for a minute; I'm going to run out and buy some stock in a lithium battery company.
One of the manufacturers of a nine volt lithium battery says in their literature that the firm spent 150 million dollars developing the battery. I guess that means that a dollar of the price for the first 150 million batteries they sell will go to amortize the development cost. Well, I'm a capitalist, so more power to them.
Lithium cells are very light in weight and have twice the voltage of most other types of cells. Where an ordinary (ordinary meaning non-lithium) flashlight sized battery is 1 « volts, a lithium equivalent will be 3 volts. That means you need only half as many cells to do the similar job (instead of a 6 foot long killer metal flashlight, now it only has to be 3 feet long...). This is a cost savings as well as a performance/size benefit. Lithium batteries have a very low rate of self discharge, meaning that they have a virtually infinite shelf life. Put them away now, pull them out in ten years and they'll be virtually as good as new. The actual figure on self discharge is about 1% per year, which from a practical standpoint is almost nothing.
Lithiums generally cost from two to four times that of lesser batteries. If they last only twice as long, you're at a break even point money wise, and you get fewer battery replacements for free.
Another advantage of lithiums is that their voltage stays constant until the thing is dead. Carbon-zinc and alkalines start with their rated voltage, and their voltage gets lower and lower as the battery is used, until the performance of whatever they're powering gets so crappy that you replace them. This isn't all that bad, as with a constant declining voltage it makes it relatively easy to build a battery level-of-charge-remaining meter. With lithiums, that's much more difficult as the voltage doesn't drop as the battery ages. Once it's dead, it's almost as if you flipped a switch and turned it off. For most electronic applications this characteristic is beneficial, as the performance of your radio, flashlight or whatever stays the same as long as it's working. But you don't get any warning before your battery is about to croak.
This lightweight, small size and very high energy capacity thing is of tremendous importance to those of us who use surveillance equipment. Usually, surveillance equipment needs to be as small as possible and have the longest battery life possible. Cost usually is not a factor as these batteries are consumed in relatively small quantities.
A body mic using a lithium battery will operate (based on our tests of a 100 milliwatt unit drawing 40 milliamps of current at 9 volts) about 3 times as long as a quality, fresh alkaline battery. No modifications to the equipment is necessary, except that lithiums cannot be recharged. If your equipment was designed to recharge its batteries, be certain no one tries to recharge lithium batteries. Hide the charger, or fill the charging connector with putty or something. You see, if lithiums have current pumped into them backwards, which is what you're doing when you charge a battery, they'll explode, sometimes violently. Then you'll sue the manufacturer of the equipment, the manufacturer of the battery and the city, and all of us will have to suffer the consequences. Lithium batteries would be more popular than they are now except for some fools using early lithiums who disregarded the instructions and had batteries blow up in their faces. Lithium batteries were yanked off the market for a while, and about the only way to get the things then was on the black market. So be absolutely certain your equipment will not try to charge the lithium batteries.
In addition to the body mic or whatever operating several times longer on lithiums, it also will work better while it is operating. An ordinary battery, as we learned earlier, starts to drop its voltage as soon as you start using it. So, on a transmitter, the power output of the unit will start dropping almost immediately. The signal will get weaker and weaker until, at some point, you consider it unusable. A lithium, though, will maintain full output power until it is completely dead, and weigh less besides. So, in addition to better battery life, you get - More Power - with the Binford Automatic, Heavy Duty, Turbocharged lithium battery (grunting noises here).
Lithium batteries also operate quite well at very low temperatures. This is a good characteristic for things like vehicle tracking transmitters or other surveillance equipment that will be exposed to outside temperatures during the winter. And, the power from the lithium battery is available immediately. Carbon-zinc and alkalines need some time to "wake up" when called upon to operate in cold temperatures. Most of the time, you as a user do not need to concern yourself with things like cold temperature operation and wake up time, as these factors will have been considered by the manufacturers in their design and specification of the equipment.
There's a lot more I could say about lithiums, but I've already exceeded the space allotted to me for this issue. Next issue, in Part 2, we'll cover rechargeable batteries and, if there's space, care and feeding. In the meantime, if there are any questions or special things you'd like covered, drop me or the magazine a line and we'll try to work it in. The magazine contact is Al Menear at 215-538-1240. Let us hear from you with comments on this or past articles, suggestions or ideas for future articles.
Copyright August 1993 by Steve Uhrig, SWS Security
Steve Uhrig is the president of SWS Security
SWS manufactures electronic surveillance, intelligence gathering and communications equipment. You may contact Steve by mail, by phone at 410-879-4035, by FAX at 410-836-1190, or by e-mail as [email protected]