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Rechargeable Batteries
Why Go Rechargeable? A Mini Series
Part 1: Why are some batteries rechargeable but others aren’t?
Part 2: The Different Kinds of Rechargeables
Part 3: Save money in the long run
Part 4: Heavy metal: Rechargeables and the environment
Part 5: Max Power: Take your rechargeable use to the next level
Rechargeable batteries abound—they’re in your laptop, cell phone, mp3 player and your car. But you may not have thought of using rechargeable batteries in your household gadgets, like your wireless keyboard and mouse, or Wii and XBox 360 wireless controllers. Every time you hear the thunk of dead batteries on the bottom of the trash can, you’re hurting both your wallet and the environment.
There are lots of reasons to use rechargable batteries in your everyday devices, but if you’re not convinced, we’ll be outlining them here over the next few days. First off, why can’t you just stick your Duracells in a charger and be done with it?
1. Why are some batteries rechargeable but others aren’t?
To answer this question, it’s necessary to review what batteries actually are. At its most simple, a battery is a unit that converts chemical energy into electrical energy. A battery holds a chemical reaction that causes electrons to flow from one of its terminals, either negative or positive, through the wiring of a device. The electrons are seeking the battery’s other terminal by traveling through the wiring and creating electricity. Northwestern University has a neat diagram and explanation here.
When any battery is placed between positive and negative terminals—that is, when it’s placed in your device—the reaction begins. Once all of the chemicals inside a non-rechargeable battery have reacted, the battery is out of power. It’s dead. Let go. Begin the grieving process.
 
However, rechargeable batteries contain chemicals that react reversibly. When rechargeable batteries receive electricity—are put into the charger—the chemical reaction inside is reversed (for the most part). This means the batteries can power your device again. Rechargeable batteries wear out only when the chemical reaction inside them can no longer be reversed by the charger.
Placing a non-rechargeable battery like an alkaline battery into a charger may give a short burst of extended use—we’re talking seconds or maybe a minute—but it may also cause the battery to leak or even explode. We are talking from experience and we don’t recommend it.
Rechargeable battery types: NiCd vs. NiMH, and why there are no Li-ion AAs
There are two types of rechargeable batteries in standard sizes: NiCd and NiMH. NiCd, which are nickel-cadmium based, were the first rechargeable batteries available to the public. They’re often referred to as “NiCads,” but that’s actually a brand name.
NiCds were first invented in 1899 in a non-portable form (kind of defeating the purpose), and didn’t enter widespread production in the U.S. until the 1960s. Your first RC car likely had NiCd batteries.
One disadvantages of NiCd batteries is that they suffer from the memory effect. This means that a NiCd that has been charged and discharged a number of times loses its charge more quickly than a newer NiCd battery. This is caused by the buildup of cadmium crystals inside the battery. To prevent this, NiCd batteries should only be placed in their chargers after they are fully discharged.
Another disadvantage is that NiCds also contain toxic materials like cadmium and mercury. For this reason, the sale of NiCds has been banned in the European Union except for select purposes.
| | Pros | Cons | | NiCd | -Lower Price | -Memory Effect
-Self discharge quickly, but not as quickly as NiMH
-Contains toxic materials
| | NiMH | -Higher total capacity than NiCd
-No memory effect
| -Self-discharge more quickly than NiCd
-Can generate more heat than NiCds
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The most common everyday use rechargeable batteries are nickel metal hydride batteries, or NiMHs. They were developed in 1989 as an alternative to clunky nickel-hydrogen batteries, which are mostly used in satellites today. NiMHs are much less toxic than NiCds. Due to their low price and relative eco-friendliness, NiMHs are currently the most popular rechargeable option.
You may know that lithium-ion (Li-ion) rechargeable batteries incased in battery packs are widely used in electronic devices like cell phones, laptops and mp3 players. Why aren’t there any lithium-ion standard-size batteries to substitute AA size alkalines? Li-ion batteries run at a higher 3.6 voltage than standard aa size batteries usually do 1.2 volts; that makes them incompatible with both your devices and battery chargers. Plus, due to the high energy and high heat potential, they need a PCB board to control current and over voltage for them to be used safely and effectively.
What about rechargeable alkaline batteries? Generally speaking, rechargeable alkalines cost as much as superior NiMH rechargeables, and have a much shorter lifespan—dozens of recharges rather than hundreds.
Save money in the long run
Over time, rechargeable batteries save so much money that they are virtually free power. Thrifty living blog The Simple Dollar, which pulls no punches, tested whether rechargeables would really save money in the long term. Blogger Trent switched from Energizer e2 Titanium alkaline AAs to Sanyo Eneloop batteries.
You can read Trent’s whole analysis at his site, but briefly, Trent spent $100.80 for 36 AAs and $47.94 for the charger, so his startup cost was $147.94. Note that Trent bought extra batteries so that he would always have some charged and ready to go. All too frequently, new users of rechargeables buy the bare minimum. Plan ahead or be left holding a dead gizmo.
He also figured that he would have to charge each battery seven times before his investment had paid for itself. With Trent’s usage pattern, that meant that it took two years before he broke even, but after that, he was coming out far ahead Trent calculated the cost of charging the batteries 120 times over the course of a year. His local electricity costs .10 per kilowatt-hour (kWh) and the charger used .02 kWh to charge each battery. With these numbers, recharging the batteries cost less than 25 cents a year! You’d pay anywhere from $75 to $150 to for120 disposable AAs.
Here’s a real life example. If you play Nintendo Wii, you may have noticed the short battery life of the Wii controller. Nintendo says that the Wii remotes should last 30 to 60 hours, but complaints abound on the net. If an average pack of four AA alkaline batteries costs $5, that’s $2.50 into the trash after every gaming marathon. Or you can pay $.004 cents to recharge your rechargeables. That’s four tenths of a cent! (By the way, Nintendo recommends only NiMHs for the Wii motes.)
If you want to get really nerdy and find out much you’d pay to charge your batteries, check out the formula here, then consult your electricity bill to find out how much you pay per kWh. From a financial standpoint, buying rechargeables may have a large start-up cost, but you’ll save money in the long run.
Heavy metal: Rechargeables and the environment
Toxic heavy metal is not what your kid brother listens to. It’s the cadmium, nickel, lead and mercury found in an array of batteries, both disposable and rechargeable, and it’s harmful to humans and animals. Runoff from cadmium mining caused deformities in animals and humans in Japan after WWII. Mercury’s toxicity is well known—it’s what made the Mad Hatter mad. Lead damages neuron connections. Even the Thomas Jefferson coin in your wallet contain a metal that is harmful when consumed in large doses and when inhaled.
If you’re not happy about the thought of tossing this stuff into a hole in the ground, there’s a two-part answer: rechargeables and recycling.
European battery manufacturer Uniross commissioned a 2007 study that claims that rechargeables are up to 32 times greener than disposables. According to the study, rechargeable batteries beat disposables by offering:
- 23x fewer non-renewable natural resources consumed
- 28x less effect on global warming
- 30x less effect on air pollution/ozone pollution
- 9x less effect on air acidification
- 12x less effect on water pollution
Also, rechargeable batteries cut down on packaging waste. The study points out that to get one kWh of energy, you can buy one pack of rechargeable batteries and its packaging or 93 packs of disposable batteries and their packaging!
Admittedly, Uniross makes rechargeable batteries and had something to gain with this study, but it’s still credible. Even the skeptics at Wired Magazine agree. The study was carried out and reviewed by two independent groups, Bio Intelligence Service and the Fraunhofer Institute.
Here’s some more food for thought: the EPA says that Americans purchase 3,000,000,000 dry-cell batteries each year. That’s three billion, with a B. (Dry cell batteries are most of the batteries we use, the main exception being car batteries.) The average American throws away eight batteries per year, which may not seem like much, but that adds up to 125,000 tons per year.
Now for the recycling component. If you live in California, AtBatt’s home state, you’re already required to dispose of your batteries responsibly. Check out AtBatt’s Battery Disposal Guide and free Battery Recycling Program. The state of California also offers resources here.
Low self-discharge batteries
If it’s been a while since you looked at rechargeables, you may remember wondering why the batteries didn’t come pre-charged. The reason is that until recently, most rechargeables lost their charge quickly when not in use. Stored on the shelf, a standard NiMH battery loses 25 percent of its power by month. Inactive NiCd batteries lose 10 percent of their power in the first 24 hours, then lose 10 percent a month.
But three years ago, manufacturer Sanyo introduced low self-discharge standard size batteries under the brand Eneloop. (How’d they do it? By improving the cathode structure and the separator. You can read a technical explanation from Sanyo here.)
In addition to their increased shelf life, this battery technology lasts through many more charge cycles than standard NiMH and NiCd rechargeables. While standard NiMHs last up to 500 charges,
The technology soon spread through the industry, and today all of the major battery manufacturers offer low self-discharge batteries.
What is mAh?
Many batteries come with a label like “2500 mAh.” The acronym mAh stands for milliampere-hour, and this number means the capacity of the battery. A miliamp is one thousandth of an ampere, or amp. (Engineer’s Edge has a good technical explanation of battery capacity). What do mAhs mean for your AAs? BatterySavers.com explains:
If you think of a battery as a small fuel storage tank, which in a sense it is, mAh is a measure of how much "fuel" the battery holds. (This is roughly comparable to using gallons to measure how much fuel a gas tank can hold. The more gallons of capacity, the more fuel the tank can hold.) With a battery the higher the mAh rating, the more electrical energy it can store. Why should you care? Some devices are like Priuses, putt-putting along slowly and evenly, with occasional accelerations. Others are like Ferraris, demanding more power and demanding it now. (Digital cameras are often in this category.) It’s important to note. A higher battery capacity will NOT overload the power of the device.
If you’re using a high-drain device—and you probably already know if you are—than mAh matters more. If your batteries have a short shelf life, a higher capacity will keep them alive longer.
Michael Bluejay has a in-depth look at electricity usage around the house here. It talks about AC (wall plug electricity) rather than DC (battery), but it’s got a lot of useful information on measuring electrical demand.
Recap
Here’s the least you need to know about rechargeable batteries:
- Rechargeables can be used between 500 and 1000 times.
- Rechargeables are better than ever thanks to the development of low self-discharge rechargeables.
- It costs about 25 cents a year to recharge 120 AA batteries. (Source: The Simple Dollar).
- Rechargeable batteries are up to 32 times greener than disposable alkalines. (Source: Uniross).
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