subject: Zen and the Art of Battery Life [print this page] Step 2: Use It or Lose It or Replace It 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.
