Zen and the Art of Battery Life

November 23, 2009 Hardware, Site News — Kyle

The lithium-ion polymer batteries shipping today are amazing creatures, packing greater energy density than both the nickel-based cells of yore and the first generation Lithium-ion cells. Yet most people are unaware of how to properly manage the life of this new technology. What you do on your laptop is your own business, but following these tips will let you do it longer (that’s what she said!). Most of this info holds true for iPod batteries as well, so you might as well learn the ropes now and reap a lifetime of rewards — at least until scientists come up with new, better, battery technology.

Step 1: Learn The Tech
LiIon cells charge in two stages. Stage one is a fast charge at constant amperage and steadily increasing voltage. When the battery reaches a 70- to 80-percent charge, the second stage begins, gradually decreasing the current applied to the battery while maintaining constant voltage until the battery is fully charged. This second stage is called the trickle, or topping-off charge, and it takes two to three times as long as stage one.

Apples charge stages graph

Apple's visual description of charge stages

Contrary to popular belief, it doesn’t matter whether you completely drain and completely charge the battery every cycle, or grab a few minutes of charge time whenever you can (with regard to battery life, at least).  But the latter practice will eventually make your reported battery-charge and remaining-life times inaccurate. To make sure the battery knows how much capacity it has, every once in a while you should completely discharge then fully recharge it. This keeps the electrons flowing through all the cells and calibrates an internal mAh counter.

Charges are cumulative, and you do not have to completely discharge the battery every cycle.

Step 2: Use It or Lose It — or Replace It
If you store your LiIon battery with a full charge, it’ll irreversibly lose about 20 percent of its charge capacity per year. If you aren’t going to use your machine for a while, leave your battery partially charged (40 to 50 percent). Even then, LiIon cells will lose capacity over time, but will do so more slowly at cool (not freezing) temperatures. Think about that when you’re choosing whether to store your old iBook in the basement or the attic.

Apple will sell you a new battery for any of its current laptops for $129, but the company no longer sells batteries for most of its older models. Fortunately for you, iFixit sells batteries for every portable Apple has made in recent memory. If you don’t get a battery from us, know that the main concern with after-market batteries is age: It’s best to buy a recently-manufactured battery and not just a “new” OEM battery that was made five years ago and has never been used.

Step 3: Gauge It
Battery capacity is expressed in milliamp-hours (mAh) or watt-hours (Wh).  The Late 2009 plastic unibody MacBook has a 60 Wh battery, so its claimed 7-hour battery life tells us that the MacBook sips just 8.6 watts. (This battery runs at 10.95 volts. Quick refresher from high-school physics: P = IV, so 60 Wh = I * 10.95 volts. Solving for current (I), we learn that this battery stores 5.48 amp hours, or about 5,500 mAh of juice.)

Your battery consumption can vary depending on how much the computer components are used (hard drive access, burning DVDs, using Wi-Fi), but the battery has a finite amount of capacity that only decreases over time.

On a Mac, you can easily determine your battery’s remaining capacity with third-party utilities such as Battery Health Monitor (shown above) or Coconut Battery, but you can also use Terminal (located within /Applications/Utilities). Type “ioreg -l -w 0 | grep Capacity”. The first item, CurrentCapacity, is your battery’s current capacity in milliamp-hours, whereas DesignCapacity lists the battery’s original capacity. System Profiler (on every Mac in /Applications/Utilities) also shows some information in the ‘Power’ profile.

Step 4: Recycle It

The Lithium inside these batteries isn’t super toxic (unlike most other batteries), but the world’s supply of lithium is finite. It’s gotten a lot more convenient in recent years to recycle batteries. Home Depot and Radio Shack will take back and recycle batteries at most of their stores. To recycle devices with integrated batteries, the fabulous e-stewards program publishes a list of certified e-recyclers that are properly accounting for their waste stream rather than shipping it overseas.

Random bit of trivia: Unused lithium batteries have been rumored to be a common source of lithium for making methamphetamines, but the ionized non-metal form of lithium used in Lithium-Ion batteries doesn’t work for this purpose.

7 Comments

  1. is it true that freezing it will make it hold more charge that what it used to?

    Comment by anju — November 23, 2009 @ 4:16 pm

  2. No, Anju, you shouldn’t freeze your Lithium-ion polymber batteries. It is true that lower, non-freezing temperatures can prolong shelf-life for for lithium-ion, NiMH, NiCad, and alkaline batteries– but don’t go too cold. Check out this test: http://www.popularmechanics.com/technology/how_to/4337496.html Battery chemistry doesn’t like super-cold temperatures.

    Comment by kyle — November 23, 2009 @ 4:20 pm

  3. I have a MacBook Pro 17 (2.93 GHz Early 2009, Model A1297). While I sometimes take it on the road, most of the time it is sitting on my desk as my main office machine, during which time it is always plugged in (sometimes for 2 or more weeks straight). Is this bad? One reason I keep it plugged in is that I have it connected to a large cinema display, and if I unplug my machine, the screen goes black. (I only use the cinema display, and keep my MacBook closed so its screen is not used). Thanks for any guidance you can provide.

    Comment by Antonio — November 24, 2009 @ 3:43 am

  4. Antonio, try asking your question in the forums or on Answers. I’m sure someone will help you out.

    Comment by kyle — November 24, 2009 @ 4:37 pm

  5. @antonio, if you’re using your mbp as a desktop machine more than a portable, I would advise you to remove the battery and keep it plugged. I have a mbp17 for which I have already lost a battery because of similar reasons. I had it plugged in all the time and rarely took it on the road. The battery got swollen and all wasted. Refer to the article above for the best way to store your battery away.

    Comment by Neo — December 5, 2009 @ 2:54 pm

  6. [...] an hour—which is guaranteed to happen with every iPhone. We’ve written extensively about Lithium-Ion batteries in the past—they’re wonderful technology, but they have a finite life of 300 to 500 cycles. [...]

    Pingback by Apple’s Latest ‘Innovation’ Is Turning Planned Obsolescence into Planned Failure « iFixit Blog — January 20, 2011 @ 3:10 pm

  7. [...] to happen with every iPhone. We’ve written extensively about Lithium-Ion batteries in the past—they’re wonderful technology, but [...]

    Pingback by Apple’s Latest ‘Innovation’ Is Turning Planned Obsolescence Into Planned Failure « iFixit Blog | I Bleed Bits - Technology for Addicts — February 2, 2011 @ 1:22 am


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