Lithium-ion battery preservation

2006-10-27

in Daily updates, Geek stuff, Science

Leaves with glowing edges

After seeing that the capacity of my iBook battery has fallen by 10% over the course of four complete cycles of discharging and charging, I went and read up on lithium-ion batteries. My previous conceptions about them turn out to be almost entirely wrong. Since almost all cellular phones, laptops, and music players with rechargeable batteries run on this sort, it is worth knowing how to keep them going for as long as possible.

1. Discharging completely, then charging completely, is not the ideal approach

Unlike other kinds of batteries, there is no ‘memory effect’ with Li-ion systems. Batteries that suffer from memory effects ‘forget’ how much charge they can hold if they are not completely drained and then completely recharged. As such, the strategy to keep them alive for the longest time is to always follow that pattern.

With Lithium-Ion batteries, full discharging is not only non-ideal, it is actually harmful. This is because it strains the weakest cell. Since a battery is composed of several cells, the failure of any one will mean the failure of the whole system. All lithium-ion rechargeable batteries have systems to prevent cell voltage from dropping too low (a microcontroller cuts it off before it reaches that point), but draining them to the point of cutoff is still harmful.

2. Temperature matters most

The biggest factor in battery life, especially for laptops, is the temperature at which the battery is kept. Judging by the figures from iStat Pro, mine is consistently at more than 40°C when the computer is running. Between reading, writing, listening to music, and just hanging around on Skype, that is probably more than twelve hours a day.

Just keeping the battery at 40°C will result in capacity loss of more than 15% over the course of one year, compared with a 2% temperature based loss if the battery is kept at 0°C and a 4% loss if it is kept at room temperature (about 25°C).

The most practical upshot of this is that it is intelligent to keep your battery outside of your computer when you are using it plugged into the wall. The most important reason for this is that it will thus be living at a much lower temperature, and thus for much longer. Since a laptop with no battery will shutdown instantly (and incorrectly) with any interruption in the external power supply, the best bet is probably to use a battery on its last legs (but still good enough for a few minutes) when plugged in, and a better one when working off battery power.

3. Storage or using at 100% charge is harmful

For reasons too complex for me to understand, a charge of about 40% is best for the long-term storage of Li-ion batteries. A Li-ion battery kept at 100% charge and 40°C will lose about 35% of its capacity in a year.

4. Li-ion batteries fail over time, regardless of anything else

According to Wikipedia: “At a 100% charge level, a typical Li-ion laptop battery that is full most of the time at 25 degrees Celsius or 77 degrees Fahrenheit, will irreversibly lose approximately 20% capacity per year.” This loss is because of oxidation (over and above heat damage, as I understand it), which causes cell resistance to rise to the point where – despite holding a charge – the battery cannot provide power to an external circuit.

For more information see Wikipedia and this page. The especially bold can learn how to rebuild depleted Li-ion batteries. Anyone with background in electrochemistry is strongly encouraged to comment on the accuracy of the above information.

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{ 15 comments… read them below or add one }

B October 28, 2006 at 12:03 am

Yours is about the last blog I thought would look like a flyer for a rave.

Milan October 28, 2006 at 12:18 am

Well, the Daily Show maintains a proud tradition of bolstering otherwise mediocre content with Photoshop.

I am just carrying on what they began.

Ben October 28, 2006 at 12:22 am

Interesting, because I’ve just bought a new phone and they recommend fulling decharging and charging the Li-ion battery. Since that was what eventually killed my old phone, I want to be extra careful.

Milan October 28, 2006 at 12:27 am

Ben,

Double check that it is lithium-ion, rather than nickel metal hydrate or nickel cadmium. Both of those have ‘memory’ problems.

Ben October 28, 2006 at 11:33 am

Yeah, definitely says Li-ion on it.

Milan October 28, 2006 at 4:03 pm

As the beginning of the above post demonstrates, lots of people are confused about how to maximize the lifespan of batteries. The consensus of websites I looked at is that the above is correct for Li-ion.

Robert February 22, 2007 at 4:53 pm

I have lithium batteries in two cameras – a Canon Ixus 850 and a Canon EOS 300 . Sometimes I do not use the cameras for weeks, even months. How can I best preserve the lithium batteries? I have been told that putting them in the deep freeze is the answer, but this seems rather drastic. As someone who is totally non technical, I would be very grateful for any suggestions from someone who has knowledge of this subject.

Milan August 15, 2007 at 12:01 am

The real-world life of my iBook battery is now less than four minutes. The heat here has done a number on it.

. December 20, 2007 at 3:04 pm

The Li-ion awakens

Dec 19th 2007
From Economist.com
New lithium-ion cells are hardier and charge faster

“Li-ion batteries, as they are known in the trade, are sensitive souls. They last only a few years, even if they are not used (one reason to check the date a laptop left the factory before you buy it). And they fade even faster when used in harsh conditions, such as high temperatures. They need special protective circuits to manage the charging and discharging (if completely discharged they can be ruined). And they may react to abuse by bursting into flames.

However, the chances of Toshiba’s new Super Charge ion Battery (SCiB) catching fire are “extremely low”, according to Toshiharu Watanabe, the head of the company’s industrial systems group. “And it will not explode even if it ruptures,” he adds reassuringly. Just as important, the battery can be recharged to 90% of its capacity in less than five minutes, instead of the hour or so required by most Li-ion batteries. And it will last for more than ten years.”

. December 20, 2007 at 3:05 pm

The most widely used lithium-ion batteries have a positive electrode made from cobalt oxide and a negative electrode made from graphite. The electrolyte (the material through which the ions pass from one electrode to the other) is a lithium-based gel or polymer.

. March 12, 2008 at 2:13 pm

* Unlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40% – 60%. Lithium-ion batteries should not be frequently fully discharged and recharged (“deep-cycled”) like Ni-Cd batteries, but this is necessary after about every 30th recharge to recalibrate any external electronic “fuel gauge” (e.g. State Of Charge meter). This prevents the fuel gauge from showing an incorrect battery charge.

* Lithium-ion batteries should never be depleted to below their minimum voltage, 2.4v to 3.0v per cell.

* Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.

* According to one book, lithium-ion batteries should not be frozen (most lithium-ion battery electrolytes freeze at approximately −40 °C; however, this is much colder than the lowest temperature reached by household freezers).

* Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.

* When using a notebook computer running from fixed line power over extended periods, the battery should be removed, and stored in a cool place so that it is not affected by the heat produced by the computer.

. November 28, 2008 at 12:54 pm

Primecell

Having the battery packs renewed by PrimeCell ran me about $60, two-way shipping included. I first used this service about five years ago and have since shipped them a total of three battery packs. The turnaround is quick (about a week, though you can pay up for 24-hr service). Not only is it less expensive than buying new ones, from my experience, the rebuilt batteries are much more powerful than OEM and they’ve also lasted 30-50 percent longer than the newer packs my Dad purchased for his drill.

. October 22, 2009 at 12:19 pm

Bolivia’s Lithium-Powered Future
What the global battery boom means for the future of South America’s poorest country.

BY JOSHUA KEATING | OCTOBER 21, 2009

The global demand for lithium, the lightweight metal used to make high-powered batteries for cell phones, laptops, and hybrid cars, is expected to triple in the next 15 years. Fifty to 70 percent of the world’s supply of this critical mineral is contained in just one place — Bolivia’s Uyuni salt flats, shown above.

. October 31, 2009 at 12:51 pm

How To Charge Your Laptop
Four essential tips for extending the battery life of your computer, cell phone, and every other gadget.
By Farhad Manjoo
Posted Friday, Oct. 30, 2009, at 5:31 PM ET

To clear up these annoyances and conflicting theories, I called up Isidor Buchmann, the CEO of Cadex Electronics, a Canadian company that makes battery-testing equipment. Buchman also runs Battery University, a very helpful Web site for battery enthusiasts and engineers. I asked Buchmann how we can make sure that our batteries last a long time… No matter what you do, your battery will become a useless piece of junk—one day it will reach a point where it can no longer be charged, and then you’ll have to recycle it. It will die if you use it often. It will die if you hardly ever use it. It will die if you charge it too much. It will die if you charge it too little. You can pull the battery out of your camera, stuff it under your mattress, and come back for it in five years. Guess what? Your battery will be dead. And when I say dead, I mean dead—not that it’s run out of juice, but that it can no longer hold a charge.

Ideally, Buchmann says, you should try to keep your battery charged from 20 percent to 80 percent. Keep in mind that these are guidelines for ideal use—it’s generally inconvenient to unplug your machine before it goes all the way to 100. But even if you’re not on constant guard, be mindful of charging your machine constantly, well past when you know it’s full. You also should be conscious of letting your battery run all the way to zero.

Try to keep your laptop as cool as possible. The best technique here is to charge up your battery when the computer is turned off. When your laptop is turned on and plugged in, you should pull the battery out of your computer. Yes, pull it out. “I know that’s inconvenient,” Buchmann says, “but keeping your laptop plugged in when the battery’s fully charged—that combination is bad for your battery.”

. October 31, 2009 at 12:54 pm

How to prolong lithium-based batteries (BU34)

The speed by which lithium-ion ages is governed by temperature and state-of-charge

The worst condition is keeping a fully charged battery at elevated temperatures, which is the case with running laptop batteries. If used on main power, the battery inside a laptop will only last for 12-18 months.

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