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Batteries for Cordless Devices—

Keep 'Em Running!

Richard Perez ©2003 Richard Perez

In this modern world, many of the devices we buy and use are available in cordless, battery powered versions. It's hard to deny that these cordless devices are easy to use, portable, and allow us to work and play far from the wall socket. This column is a short guide to selecting the right kind of cordless battery technology, how to break the battery in, and how to make it perform well and last long.

Selecting the Device

A happy cordless experience begins when you select your cordless device. This information applies to all battery powered devices—laptop computers, cell phones, digital cameras, camcorders, cordless power tools, portable stereos and TVs, flashlights, radios, and any device powered by its own internal battery.

When buying a device, it is easy to become focused on the device itself and what it does. When you choose a cordless device, be sure to investigate what type of battery technology is used to power it. An antiquated battery technology can easily make the device an expensive pain to use.

In many instances, the battery is specifically made and sized to fit within the device. Examples of this are laptop computers and cell phones. Here you are stuck with the battery that the manufacturer has built into the device. If it comes with a proprietary battery, there's little you can do to choose what battery technology is employed. If you are comparing devices, make the battery technology employed a prime criteria.

Other devices use standard removable and rechargeable cells, such as the common AAA, AA, C, or D sized cells. If the device you own or plan to buy uses standard removable cells, you can easily use the battery technology of your choice.

Battery Types

Three types of rechargeable batteries are now commonly employed in portable devices—lithium ion (Li-Ion), nickelmetal hydride (NiMH), and nickel-cadmium (NiCd). Each of these technologies has distinct characteristics.

Lithium ion. Li-Ion technology is the new kid on the block. The use of this technology in consumer devices is less than four years old. Li-Ion cells are not yet found in standard flashlight battery sizes. The reason for this is twofold—cost and battery voltage (around 3.6 VDC per cell, making it unsuitable for most devices employing flashlight-sized cells). Li-Ion, however, has found its way into proprietary batteries powering laptop computers, cell phones, and camcorders.

Of all the current rechargeable battery technologies, Li-Ion is the one to choose if you have the choice. Li-Ion has the highest energy-to-weight and energy-to-size ratios—your device will run longer, weigh less, and be smaller in size. Li-Ion has only minimal "memory effect." Memory effect is the tendency of a battery to lose its capacity to store energy if it is routinely shallow cycled. Li-Ion technology also doesn't use any heavy metals and is environmentally friendly.

Nickel-metal hydride. NiMH technology is now common and has been used in consumer devices for more than five years. NiMH cells have a voltage of 1.2 VDC and are found not only in proprietary battery packs, but also in standard flashlight cell sizes. NiMH cells are energy dense, about double the capacity of similarly sized NiCd cells, but not as energy dense as Li-Ion cells. NiMH cells have only a slight memory effect, and employ no heavy metals.

Nickel-cadmium. Many cordless power tools still come with factory supplied NiCd batteries. Avoid them. These cells have three major deficiencies. First, NiCd has the lowest energy density of any rechargeable battery technology employed in portable devices. Second, it has a radical and profound memory effect. Third, it employs cadmium, which is a heavy metal that is dangerous to our environment and must be specially disposed of or recycled.

When you're shopping for cordless tools, spend the extra money on a NiMH battery, which is sometimes an option. Soon, most tools will at least have NiMH as an optional replacement battery. Within a couple of years, most tools will come with NiMH as standard.

Breaking in a New Battery

How you cycle your cordless device when you first use it has a large effect on its battery's performance and longevity. New batteries need to undergo a "forming" process—breaking in. This applies to all the battery technologies—Li-Ion, NiMH, and NiCd. When first using the device, make sure to deeply cycle the battery for at least five cycles. Deep cycle here means to operate the device until the device ceases to function normally. This will assure that the battery is "formed" for its maximum capacity Failure to do this will result in a battery with less effective energy capacity and a shorter lifetime.

Routine Cycling

With devices using Li-Ion and NiMH batteries, it is prudent to fully discharge the battery every thirty shallow cycles, or every month or so. While these technologies are ozonal notes touted by the manufacturers as having no memory effect, experience has shown that they do have a slight memory effect. Deep cycling the battery every month or so will keep them working at peak capacity.

NiCd batteries should be deep cycled every three to five cycles or they will lose their capacity to store energy. It is sufficient to use the device until it ceases to provide normal functionality. The practice of operating the device until the battery is totally dead will reduce battery capacity and longevity.

For example, when a flashlight becomes dim, it's time to recharge the battery. Don't wait until the lightbulb goes totally dark. Don't place a rubber band around the trigger of your cordless tool and run it until it stops rotating. Just use the tool until it begins to slow down and provides reduced function. Batteries are composed of series connected cells. If a battery is run to zero volts (utterly discharged), one or more cells may become reverse polarized, resulting in a permanent loss of capacity.

Recharging the Battery

Many cordless devices come with a charger supplied by the manufacturer. Examples are laptop computers, cell phones, and camcorders. These devices have a microprocessor that determines when the battery is fully charged. They require very little attention from the user and are generally quite effective at determining when the battery is fully charged. Experience has shown that leaving these devices under charge continually (24/7) will reduce battery capacity. In other words, when the device claims that it is fully charged, it probably is. It should be disconnected from the charge source if the device is no longer in use.

In devices that have removable flashlight-sized cells, recharging is more vague. Often the charger supplied by the manufacturer is designed for low cost rather than for maximum battery performance and longevity. A good way to determine if the factory-supplied charger is of high quality is to feel the cells at the end of their charge cycle. Are the cells hot, or even warm? If so, it's time to look for another charger. Modern, microprocessor-based chargers will refill standard-sized cells without overheating them. See the "Things that Work" article about the C. Crane charger in HP86 as an example of a high quality, standard-sized, cell charger. Cell overheating reduces cell life and is the hallmark of a bad charger.

Some Notes on Specific Cordless Devices

All devices are not created equal. Here are specific tips for some of the more common cordless devices you may own.

Laptop computers. Perhaps the laptop represents the greatest payoff for proper battery treatment. Replacement batteries for laptop computers cost in the hundreds of dollars. Proper treatment can yield long battery life and big savings. The goal here is to see if you can make that original laptop battery last until you are thinking of replacing the computer because the computer itself is obsolete.

First off, if you have a contemporary laptop, you probably have a Li-Ion battery. This means that you have a highly energy dense battery with minimal memory effect. Following three simple rules will make that battery last until you replace the computer.

1. Form the battery with five complete deep cycles when you first take the computer out of the box.

2. Cycle the battery until the computer shuts down, at least once a month.

3. Don't leave the computer plugged into the AC mains 24/7. When you aren't using the computer, switch off the power supply/charger.

Cell phones. About 50 percent of the size and weight of a modern cell phone is the battery. Here is a good place to spend the extra bucks for the best battery you can possibly get. If the cell phone comes with a Li-Ion battery, great; if it doesn't, buy one. The whole reason for a cell phone is the function and convenience of cordlessness. Why place this function at the mercy of a dead battery?

Be sure to give the battery a forming regime when you first get the phone. After that, don't neglect to give it a monthly deep cycle. Don't leave it plugged into its charger all the time. When the recharge cycle is done, disconnect the charger.

Digital cameras. No device seems to suck batteries flat as quickly as a digital camera. Most of these are set up to use standard-sized flashlight cells. The only type of cells to consider using in these devices is NiMH. Most chargers supplied with cameras are designed to be cheap, not smart. Consider buying a smart charger for your camera's cells.

Cordless power tools. NiMH batteries will last longer and deliver better service, so make them your first choice whenever possible. Once again, since you are locked into the factory-sized battery pack, give the battery a forming charge. Cycle it completely every month if it's NiMH and every few cycles if it's NiCd, and don't leave it under charge all the time.

Storing Cordless Devices

If for some reason you are not using your battery powered device routinely, store it properly. Recharge the battery completely and remove it from the device before storage. Recharge the battery before reusing the device. Doing this will ensure long battery life.

I hope this article will help you select and use cordless devices better. I welcome feedback from battery powered users. Share the info, and we all benefit.


Richard Perez, Home Power, PO Box 520, Ashland, OR 97520 • 541-941-9716 • Fax: 541-512-0343 • [email protected]


"Don's death is a loss to this entire planet... His spirit lives on!"

Don Kulha died on May 6, 2003. He was 52 years old. Don was Home Power's CD-ROM dude. If you spin up one of HP's CDs on your computer, it's because Don made it happen.

I first met Don when Home Power was young, around 1989. He was one of the early computer freaks, and was operating one of the very first computer bulletin board systems anywhere, out of Sonoma County, California. He wanted to put Home Power files on-line, and I agreed. Later, totally under his own steam, he produced the very first CD-ROM containing data from Home Power magazine. This earned him a permanent position on our crew.

Don was a complex guy, a product of the San Francisco-based consciousness revolution of the mid-1960s. His interests were as wide as the universe and his limitless imagination. He was a believer in us poor humans and in the fragile fate of this planet.

Don wore many hats in his short time here—race car mechanic and motorhead, technoid, NASA space mirror transport coordinator, computer geek, bon vivant, rock star groupie, solar energy user and enthusiast, cranky perfectionist, vidiot, Ham radio operator and emergency communications coordinator, electronics homebrewer, and always, and most important, sterling dad to his beloved son Alex.

Don was my friend. Many times, we sang the fifty-year-old hippie's lament—if I had known I was going to last this long, I'd have taken better care of myself I can remember the many mornings we'd solve this small planet's problems over smokes and cups of strong coffee laced with Kahlua. Don had vision and he had hope. Don also had his darker side, succumbing to the hipster's disease of paranoia—his Y2K food stash probably outlives him.

Don held the position of "Captain Trips" during many of Home Power's road excursions. Because of his levelheaded and rock-solid road experience, I entrusted him with the lives of our crew. While the crew may have grumbled about his penchant for slow speed and truck stop food, they survived—we had no accidents on the road.

Don's death is a loss to this entire planet—all of us are diminished by his passing. His spirit lives on!

—Richard for the entire Home Power crew


"C. Crane's QuickCharger is the best v battery charger I've ever used." gfc,

— Richard Perez, Things That Work!, Home Power #86

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