For electronics, portability usually requires battery power — or a very, very long power cord. Even solar-power aficionados rely on batteries to store excess energy through the day. Batteries are everywhere and in every sort of device, and it seems there's a new type of battery every month! This chapter reviews the different battery types so you can decide what battery is right for the job.
All the jargon associated with batteries makes a whole lot more sense if you know a little about what makes a battery go. In the simplest terms, a battery is a device that produces electricity through a chemical reaction. The interaction between self-contained chemicals is what makes batteries work; it's unnecessary to tap into another power source (such as a wall socket) when you use a battery. You increase the versatility and portability of your electronic devices when you use batteries — especially long-lasting batteries. You use several items every day that have batteries — your car, you laptop computer, your mobile phone, or your digital camera. Although you don't have to know chemistry to understand why batteries are important, you should know a little something about how (and how well) they work because you can waste a lot of cash on inefficient batteries.
Tip
You can find a much more complete description of battery operation at http://science.howstuffworks.com/battery1.htm.
Standard voltage of alkaline or carbon-zinc batteries varies from 1.2 – 1.5V. The rectangular 9-volt (9V) battery is really made from six 1.5V batteries connected end-to-end so their voltages add up to 9V. Lead-acid batteries, such as those used in a car or a gel-cell, provide 2V per cell. Putting six of them together end-to-end makes a 12V battery, which is standard for automotive use. Batteries made with lithium have a characteristic voltage of 3 – 3.3V. These are just a few examples.
Batteries come in different sizes and shapes because they have different jobs to do (see Figure 15-1).
Batteries have two primary ratings that you'll need to keep in mind to choose the right type for your circuit:
Characteristic voltage: The relatively constant voltage between the two battery terminals. This measurement is based entirely upon the chemicals used to transfer electrons. (See the sidebar, elsewhere in this chapter "How Batteries Work," for more information on characteristic voltage.)
Energy capacity, measured in ampere-hours or Ah: Because a battery's characteristic voltage is relatively constant, the only change between a little battery and a big battery of the same chemistry is how long the battery can supply current before it dies or requires recharging. If you multiply ampere-hours by the battery voltage, you can calculate watt-hours (watt-hours are the units of measurement used on most electric bills). The higher the capacity in Ah, the longer the battery will be able to supply current to your equipment while maintaining its rated voltage. More Ah equals more operating time.
If a battery can supply one ampere of current for an hour before exhausting its chemicals, it's rated at 1 Ah. A rechargeable Ni-Cad battery with a rating of 1200 mAh can supply 1200 mA (or 1.2 A) for an hour. The actual rating is more complicated than that, but you get the idea. Table 15-1 in the next section shows a number of common battery sizes, chemistries, and energy ratings.
With some kinds of batteries, when the chemicals have transferred all their electrons, that's it; the battery is dead. Those are disposable or non-rechargeable batteries, also referred to as primary batteries. Other batteries are rechargeable, which means the chemical reaction can be run in both directions; one way creates electricity (called discharging) and the other way stores energy (called charging). These types of batteries are also known as secondary batteries.
Warning
Don't try to recharge a disposable battery because the chemicals just won't change back to the way they were. Attempting to recharge a disposable battery runs the risk of heating up the battery or causing major corrosion. They can even explode if the heating causes gas to build up inside the battery.
Disposable batteries and rechargeable batteries each have their own merits, which are discussed later in this chapter. If you're trying to decide between the various battery types, try regular, old-fashioned disposables and see how long they last. If you find that they die within a few days or weeks, you should really consider the more expensive rechargeable options.
Tip
Eventually, all batteries must be disposed of. Even rechargeable batteries eventually die. Be sure to keep extras around even if you rely primarily on rechargeable, longlife batteries.
Table 15-1. Common Battery Types and Ratings
Battery Style | Chemistry | Voltage (with a Full Charge) | Energy Rating (Average) |
|---|---|---|---|
AAA | Alkaline (disposable) | 1.5V | 1200 mAh |
AA | Alkaline (disposable) | 1.5V | 2600 – 3200 mAh |
Zinc-Carbon (disposable) | 1.5V | 600 – 1200 mAh | |
Nickel-Cadmium (Ni-Cad) (rechargeable) | 1.2V | 600 – 700 mA-hr | |
Nickel-Metal Hydride (NiMH) (rechargeable) | 1.2V | 1500 – 2200 mAh | |
Lithium-Ion (Li-Ion) (rechargeable) | 3.3 – 3.6V | 2100 – 2400 mAh | |
C | Alkaline (disposable) | 1.5V | 7.5 – 8.5 Ah |
D | Alkaline (disposable) | 1.5V | 14 – 22 Ah |
Alkaline (disposable) | 1.5V | 580 mAh | |
Nickel-Cadmium (Ni-Cad) (rechargeable) | 7.2V | 110 – 125 mAh | |
Nickel-Metal Hydride (rechargeable) | 7.2V | 150 – 175 mAh | |
Coin cells | Lithium (disposable) | 3 – 3.3V | 25 – 1000 mAh |
Tip
One factor in evaluating the quality of any battery (rechargeable and disposable alike) is the battery's discharge curve. In Figure 15-2, a graph represents how battery voltage changes as its energy is used up. A perfect battery would provide a constant voltage (represented in the figure as a horizontal line) until it's completely exhausted, and then drop vertically to 0 voltage. Real batteries try their best, but can't quite meet that standard. As they're discharged, their output voltage gradually drops to about 80 to 90 percent of the full-charge voltage. At some point, their output voltage starts to drop rapidly. If you think of the discharge curve as representing a battery-powered flashlight's brightness, you get an idea of how the battery performs as it's discharged.
In Figure 15-2, the two performance leaders are alkaline batteries (which are disposable) and NiMH batteries (which are rechargeable). The following sections rate all battery types, categorizing performance and cost effectiveness.
You're probably most familiar with disposable batteries; after all, the alkaline battery has been immortalized by Energizer bunnies and Coppertops since the 1960s. Here are ratings for the two most common disposables around.
Zinc-carbon batteries are a familiar type of disposable batteries. They're an obsolete type of chemistry and I don't recommend them. Although they function fine for a while, they have relatively short lives and often corrode. Between the rod and case of each zinc-carbon battery is a paste saturated with a weak acid — the very same acid that leaks out and ruins your flashlight when you leave discharged batteries inside. All in all, this is not a winning combination.
Zinc-carbon batteries show the most voltage drop as they're discharged. A flashlight using zinc-carbon batteries dims noticeably as the batteries grow weaker. Although this may be okay for a flashlight (although it's not optimal), most electronic devices need a constant voltage to work well.
Tip
If a battery's voltage drops too quickly, many devices will turn off before the battery's energy is completely used. If possible, use a more robust battery type.
Strength | Inexpensive |
Weaknesses | Low energy rating and high voltage drop when discharged |
Energy capacity drops at low temperatures | |
Not rechargeable and often corrodes when discharged |
The alkaline battery is a disposable battery type whose chemistry is a big improvement over zinc-carbon. It uses an alkaline solution that's much less corrosive than the weak acid used in zinc-carbon batteries. Alkaline batteries also have a much higher energy density than zinc-carbon batteries, meaning that more energy is packed into the same volume. You can see evidence of this by reviewing the higher Ah ratings for alkaline batteries in Table 15-1.
The alkaline battery's discharge curve is much flatter than that of the zinc-carbon battery; the output voltage stays steady until a lot more of the stored energy is discharged. Because it contains more energy to begin with, the alkaline battery runs electronic devices for a much longer time than the zinc-carbon battery.
Strengths | Widely available with a high energy rating |
Does not corrode | |
Weaknesses | Expensive when used continuously |
Not rechargeable | |
Heavier than alternatives |
Warning
Disposable batteries contain chemicals that aren't exactly poisonous, but aren't good for the ground or water supply. Instead of throwing away your dead batteries, ask your local recycling center, electronics shop, or hardware store whether they can be recycled as described at the end of this chapter.
Rechargeable batteries generally give you the best of all possible worlds. They have long lives and are also rechargeable. Of course, not all rechargeable batteries are created equal, and cost is a consideration. The following sections sort through the issues and benefits of these batteries.
The nickel-cadmium battery (Ni-Cad) was the first popular rechargeable battery type and is found in all sorts of rechargeable appliances, such as toothbrushes, drills, cordless and mobile phones, and model cars. Nifty as they are, there are better alternatives.
Warning
Cadmium is a toxic metal; although individual batteries pose no danger when used in electronic devices, after the battery finally dies you're faced with disposal problems in landfills. Cadmium can be leached into the ground soil, and this is not a good thing. (See the section in this chapter, "Safely disposing of batteries," for more information about proper battery disposal.)
Ni-Cad batteries (often pronounced "NYE-cad") have a decent energy rating, but they don't last as long as alkaline batteries. Their discharge curve is a little weak towards the end of charge, but they can be recharged many times at little expense. Ni-Cad batteries can also supply high bursts of current and that makes them a popular choice for cordless power tools.
Early generations of Ni-Cads had a memory effect that gradually reduced the battery's energy rating when recharged unless special conditioning was performed. The Ni-Cad batteries sold today are largely free of that problem. For low-power devices, Ni-Cad batteries are fine, but don't get too used to Ni-Cads; they're being phased out in favor of NiMH (nickel-metal hydride) batteries except where high discharge currents are needed, such as for power tools.
Strengths | Medium energy rating |
High discharge current | |
Low cost | |
Rechargeable | |
Weaknesses | Slight memory effect over many charge/discharge cycles is still possible, although this problem has been largely fixed |
Cadmium is toxic when disposed of improperly | |
Lowest energy density of rechargeable battery types |
Nickel-metal hydride (NiMH) batteries were developed to better meet the higher power delivery demands of modern electronic gadgets like digital cameras, portable computers, and audio players. The cadmium used in Ni-Cad batteries is replaced with a compound of hydrogen and other metals — voilà, no more toxic metal. Additionally, overall battery performance is greatly improved.
NiMH is the first rechargeable battery type to exceed the alkaline's energy density. As a result, these batteries are rapidly displacing Ni-Cads. NiMH batteries hold their output voltage nearly constant for much longer than the Ni-Cad and are comparable to the performance of top-quality alkaline batteries.
NiMH battery chargers have become quite inexpensive and can recharge battery cells in just a couple of hours; this battery is highly recommended. They'll pay for themselves in no time!
Strengths | Excellent energy density |
Can be recharged quickly and for many cycles without "memory effect" power loss | |
Less toxic waste to dispose of | |
Weakness | More expensive than alkalines |
The next step in battery development, Li-Ion batteries can be recharged many times over. These cells are often combined into battery packs and used to power laptop computers. They're just becoming available as separate cells.
Strengths | Excellent energy density |
Can be recharged quickly and for many cycles | |
Weakness | Most expensive of rechargeable types |
If you need a lot of energy, only a lead-acid battery will do the job. Although the lead compounds and strong acid electrolyte pose some toxicity problems, these batteries are inexpensive to manufacture and easy to recycle. You can see why this has been the battery of choice for most high-power uses for nearly 100 years.
Luckily for battery users, the hazards of the acidic electrolyte have been reduced with the creation of the gel-cell battery. Instead of a liquid, the acid is contained in a gel that prevents spillage with only a small loss in energy rating. The gel-cell is a safe and effective means of providing long-term energy storage.
Strengths | Good energy density and inexpensive |
Can be recharged many times | |
Weaknesses | Heavy |
Toxic materials and dangerous electrolyte require proper disposal |
Many electronic gadgets come with or accept an assembly containing several individual batteries that are permanently wired together. These battery packs can be made to fit almost any shape required and in a variety of voltages.
If you crack open the case of a dead battery pack, you'll find several cells connected end to end in a series with welded tabs. It's generally not practical for the hobbyist to rebuild battery packs, but often they can be traded in or recycled.
Some tools and two-way radios are designed to accept battery packs of several different voltages, varying their output power as the voltage changes. You can choose a lightweight pack with a low energy rating or a heavier pack that gives more output.
Tip
For my own use, I try to have one or two of each type of battery pack.
Here, in no particular order, are some good ideas for getting the most out of your batteries:
Buy disposable batteries in bulk. Buying alkaline batteries four at a time at the grocery store is convenient (and may seem less expensive at the point of purchase), but in the long run, it's incredibly expensive. Warehouse stores and online suppliers often have bulk packs of 50 or more batteries at a fraction of the price per battery if you were to buy them in small quantities.
Refrigerate spare batteries. Because a battery is a chemical device and chemistry runs slower at lower temperatures, you'll prolong the life of your batteries by keeping them cold. Don't freeze them! The water in the electrolyte will expand and possibly crack the case, ruining the battery.
Always have a spare. When buying batteries, always have extras for emergencies and periods of prolonged use. Don't be caught discharged!
Tip
Because batteries allow you to take your gadget with you on the road, you should be extra diligent about bringing spares with you. Who knows when and where you'll find a plug for your charger?
Group rechargeable batteries in sets. A set of batteries is only as strong as its weakest cell, so try to keep the set together as they age. Battery suppliers sell inexpensive plastic cases that hold a few batteries. Don't let one weak cell spoil the whole set.
Regularly condition rechargeable batteries to help keep them in top shape. If you have several sets of batteries or battery packs, rotate them through a charge/discharge cycle on your charger every few months.
Used properly, a battery is a safe and effective way of storing electrical energy. However, a battery stores a lot of energy and uses concentrated chemicals to do so. Remember that!
Letting the energy out too quickly can wreck the battery — and wreck whatever it's connected to. Exposing the chemicals or putting them under too much stress can result in danger to you and damage to the battery.
To get the longest life and best performance out of your investment in rechargeable batteries, you should use a charger designed specifically for that battery type. For example, a Ni-Cad battery charger won't properly charge NiMH batteries. An improper charger may even damage the batteries or be damaged itself.
Warning
Good advice in any setting (not just batteries) is to do what the manufacturer tells you to do. The manufacturer wants you to have good results with its batteries and to be safe when using them (after all, that's the best way to get you to buy them again). Don't try to speed up battery charging with a high-power charger if the batteries aren't rated for it. Limit discharge current to within the battery's ratings. Use chargers on the batteries they're intended for. The reward for "pushing the envelope" is rarely worth the risks.
Here are some important things to remember:
Set your smart battery charger to the correct setting. Smart chargers have a specific method of charging, called a charging algorithm. They're able to sense the battery's charge level and adjust the rate of charge so charge time and stress on the battery are minimized. The optimum algorithm varies with battery chemistry so Ni-Cad and NiMH batteries should be charged differently. If you have a smart charger, be sure it's set for the right battery type.
Promptly remove charged batteries from your old-style battery charger. Old-style battery chargers just apply a certain amount of current to the battery until you remove it. Leaving a battery in such a charger can overheat and ruin a battery. Take care that batteries are removed promptly when charged.
Follow the battery manufacturer's guidelines for charging and obtain a proper charger if necessary. A lead-acid battery charger must be able to switch to trickle charge or float charge automatically when full charge is reached. This keeps the battery at full charge without overcharging it.
Let your batteries run down every so often. It does not damage Ni-Cad and NiMH batteries to be completely discharged. In fact, regular 100 percent discharges help to restore the battery chemistry. Good chargers first discharge these batteries before charging them back up.
Treat your lead-acid batteries right. Deep-cycle lead-acid batteries, such as those intended for RV and marine use, are also able to withstand an occasional deep discharge. (They work best, however, if never discharged to below 50 percent of capacity.) Regular automobile batteries, however, are not made for that type of use and will be damaged. Only completely discharge batteries that can handle it.
Don't stress out your batteries. Batteries can also be stressed by discharging them too rapidly. Short-circuits and excessive loads can wreck internal connections and cause electrolytes to boil or vaporize. This type of use calls for special batteries with adequate current surge or pulse ratings.
Here's a short list of do's and don'ts to follow when you're handling batteries.
Don't freeze a battery. The water in the electrolyte may expand, cracking the case.
Don't expose a battery to excessive temperatures. High temperatures may result in too much pressure inside the case or damage to the chemicals.
Do keep batteries clean, dry, and off wet floors or shelving. Keeping batteries from getting damp and dirty prevents slow discharge across the battery's surface.
Do use compounds that prevent terminal corrosion for any lead-acid battery that you store or use in an exposed location.
Do take special care with wet cells, such as car batteries. These batteries may leak small amounts of acidic electrolyte that can damage unprotected supports.
Warning
Batteries pack a real punch when it comes to delivering current. Even AA batteries can put out several amperes if short-circuited. This amount of energy is enough to make a battery hot enough to burn you or melt a small wire. Larger batteries can get hot enough to explode when they're short-circuited. A large lead-acid battery can start a fire or melt a tool when short-circuited with the potential for serious burns. Respect the energy. Protect battery terminals against accidental short circuits. For larger batteries, keep terminal protectors installed at all times.
The chemicals that give batteries their great energy storage ability are also fairly toxic or corrosive. Don't throw old batteries in the trash where they wind up corroding in a landfill, leaching chemicals into the water supply — it may actually be illegal in your area! Hardware stores and battery stores will often recycle your old batteries, including alkalines, and often for free or a small fee. Your municipal or county government may also have a recycling program for batteries. Check www.batteryrecycling.com for more ideas.