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NiMH batteries, Alkaline Batteries

Battery Technology.

Batteries contain chemicals, and the particular combination of chemicals inside a battery determines its technology. The most common battery technologies for household or consumer products are alkaline and NiMH.

Alkaline batteries have been around for more than 50 years and account for the vast majority of batteries made and used in the U.S. They're very energy intensive, but the charge degrades gradually whether sitting idle or in operating mode. Alkaline batteries are low-drain devices with a long shelf-life (usually five to seven years, sometimes longer) and are well-suited to applications used intermittently, such as flashlights, and to devices with relatively low energy requirements, such as clocks and TV remotes; alkaline batteries can be used in digital cameras, as well, but there are better alternatives (see below). As "primary" cells, alkaline batteries cannot be recharged once depleted. Our picks for the best cheap alkaline batteries are the Duracell CopperTop AA (starting at $10/20-pack, Amazon) and Rayovac AA Alkaline (starting at $10/30-pack, Amazon).

By the way, a new type of rechargeable alkaline battery recently hit the market, but experts aren't sold; they point to the very limited number of recharges the battery can take (a few dozen) and the drop-off in electrical potential (voltage) with each recharge.

NiMH batteries, introduced in the 1990s, have supplanted nickel-cadmium (NiCD) batteries as the preferred technology for consumer applications that draw lots of energy (i.e., high-drain devices), such as digital cameras and power tools. Like NiCD batteries, NiMH batteries are rechargeable but far surpass the older technology in terms of energy capacity. The upfront cost of NiMH batteries is about twice that of alkaline batteries, and the cost of a charger specifically for batteries (a must) will set you back another $15-$20. But the current crop of NiMH batteries can be recharged hundreds of times for mere pennies a charge; given the price of replacements, you should recoup your investment quickly. (Hint: Recharge before the battery fully drained to prolong its useful life.) Our runner-up pick for best cheap NiMH battery is the Sony Rechargeable AAA 900mAh (starting at $8.60/4-pack, Amazon), which can be recharged up to 300 times. The Energizer Rechargeable D 2500mAh (starting at $10/2-pack, Amazon) has a recharge capacity of 100 times.

The downside of these so-called secondary (rechargeable) cells is their high rate of self-discharge. NiMH batteries degrade quickly, meaning shelf-life is limited -- especially if not stored at sufficiently cool temperatures. Green Batteries says a NiMH battery will give up as much as 40% of its charge within 30 days when sitting in 70-degree heat and continues losing capacity as time passes. Regular NiMH batteries must be charged before first use.

A relatively new technological advance is the low self-discharge NiMH batteries that come packaged already charged up. Although consumers and experts suggest giving the battery a charge before its maiden voyage -- pre-charged batteries may not be fully charged when leaving the factory and do lose some juice between there and your home -- the shelf-life of pre-charged NiMH batteries is a few years rather than months. Our pick for best cheap battery, the Sanyo Eneloop AAA NiMH Pre-charged 800mAh (starting at $9.50/4-pack, Amazon) claims to hold 75% of its capacity after three years of sitting idle and can be recharged up to 1,500 times. Low-self discharge batteries are quite versatile. Because the technology holds capacity far longer (remember, cool and dry storage conditions are critical), experts say it's an acceptable substitute for alkaline batteries and suitable for high-drain devices used intermittently.

The most common sizes for alkaline batteries used in consumer products are AAA, AA, C, and D. Rechargeable NiMH batteries for the home market come in the same sizes. One size battery cannot be substituted for another, so be sure to read the owner's manual. Sometimes alkaline and NiMH batteries are interchangeable -- it depends on the application -- but experts note that replacing multiple alkaline batteries with multiple NiMH batteries in a device gets tricky because of the difference in electric force. (See the section on power below.) Traditional alkaline batteries can be thrown into the garbage, but for safety reasons it's best to dispose of one or two at a time. NiMH batteries must be recycled.

Other battery technologies that occasionally pop up in reference to consumer products are lithium and lithium-ion. Lithium batteries have about double the energy capacity of alkaline batteries and a longer life span. They also cost more and must be recycled. Lithium batteries are often used in medical devices like pacemakers and hearing aids, as well as PDAs and watches. Lithium-ion batteries are rechargeable and boast a longer shelf-life than the NiMH technology. For any given size, Li-ion batteries have a higher energy density and voltage than other rechargeable technologies. Lithium ion batteries are typically found in consumer electronics, like laptops and cell phones.

Batteries Power.

Batteries are little storehouses of energy waiting to be released. All it takes is connecting to a device, which completes the circuit and sets off an internal electrochemical reaction that unleashes the energy and powers up the device. The amount of energy a battery can discharge over a period of time -- i.e., battery capacity -- is denoted as milliampere hours, or mAh. The unit of electric potential is called a volt.

Put differently, the chemical composition of a battery affects how much energy it can store/discharge, and the power needs of the application affect how quickly the energy is used up. How long it takes for a battery to run down (i.e., service hours) depends on the device to which it's connected.

Batteries with the same internal chemistry (alkaline batteries, say, or NiMH batteries) produce the same number of volts regardless of size. Alkaline batteries produce 1.5 volts (a 9V alkaline battery is merely a housing for four 1.5V cells strung together) and NiMH batteries produce 1.2 volts. (Beware of substituting several NiMH batteries for several alkaline batteries; the total voltage may not be sufficient to power the device.)

The number of milliampere hours, however, varies by the particular battery model, and a higher mAh indicates it's likely to last longer (depending on the application, of course). According to Wikipedia, capacity for AAA batteries is usually 1200mAh and 2700mAh for AA batteries. (Not all alkaline battery casings or packaging specify the mAh.) Alkaline batteries lose charge (voltage) at a relatively slow, steady rate and their useful life is pretty much over when the electric potential sinks to about 1.1 volts, which is approximately the minimum necessary to keep most devices running.

The energy capacity of NiMH batteries also varies by size and manufacturer. Again according to Wikipedia, that would be 800-1000mAh for AAA batteries and 1700-2900mAh for AA. The mAh on pre-charged NiMH batteries also varies; an older Sanyo Eneloop AAA model boasts 2000mAh while the latest version on our list claims 800mAh. NiMH technology depletes at a steady rate until suddenly there's insufficient juice to power a device; again, at about 1.1 volts. Experts caution that the charge often depletes faster than the mAh rating would suggest, so keep that charger handy.

by Maralyn Edid (Google+ Profile)

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Energizer Rechargeable D Review
Sony Rechargeable 900 mAh Review
Rayovac Alkaline Review
Sanyo Eneloop Pre-Charged Rechargeables Review
Duracell CopperTop Alkaline Review

 

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