The Straight Dope®

Are titanium batteries really better than alkaline? Or is this some sort of new marketing ploy? —Beth Hanes, via e-mail

I've been pointing those who claim "battery memory" as truth toward your archive for quite a while, but the true believers insist, "He was talking about nicad batteries. Nickel metal hydride batteries are different." Common wisdom around here is that NiMH batteries will get battery memory and should always be fully discharged/fully charged, whilst lithium-ion batteries don't and can be happily discharged/recharged at any time without worry. Any chance you can revisit your old column and update for today's battery technology? —Jeff Fenstermacher, via e-mail

Certain parties are now thinking: I don't need to trouble myself with these technical minutiae. We'll see what they think next time the laptop catches fire.

It's been a few years since I wrote about batteries, during which time the technology has made great strides and the hype has advanced even faster. Titanium batteries, for example, aren't a miraculous breakthrough in energy storage, just an improvement in both disposable and rechargeable batteries. Basically, small amounts of a titanium-containing compound are added to a battery to improve performance—to judge from the patents, mostly by lowering internal resistance. Lower resistance means less juice is lost as heat, leaving more to operate the CD player, vibrator, etc. Tests comparing titanium-enhanced batteries with the ordinary kind generally show improved performance, although you still don't get as much power as from a lithium battery. Then again, lithium batteries cost maybe two and a half to three times what standard alkalines do, whereas the titanium premium is on the order of 20 to 40 percent. For high-drain applications like digital cameras, or where you need exceptionally long life (computer memory backup, for example), lithium is the best choice. Otherwise, titanium batteries are worth a look.

On to rechargeable batteries. In 1999 I wrote about nickel-cadmium (nicad) battery memory, a common term for the seeming tendency of a nicad battery that's been charged too many times without being entirely drained to remember where it was drained to and eventually not take a full charge. I pointed out that such cases aren't examples of true battery memory, a real if rare phenomenon, but rather something called voltage depression—though the total energy stored in the battery is unchanged, it doesn't come out with as much force as before. Admittedly this is something of a fine point, since the net effect is the same—you get less use out of the battery per charge than you once did. Voltage depression in nicad batteries stems from an unfortunate characteristic of the cadmium hydroxide crystals that normally form as the battery discharges. The crystals start out small when the battery is new, then grow over time, increasing internal resistance and reducing power output. Most practical solution I've heard: periodic deep discharge followed by normal charging to full power, breaking the big crystals into little ones.

What I said in 1999 still holds true for nicad batteries, but since that time two other types of rechargeable batteries have become popular: nickel metal hydride (NiMH) and lithium ion. (Just so we're clear, lithium ion is different from the nonrechargeable lithium batteries discussed above.) A NiMH battery can store 30 percent more energy than a nicad of equal size, but it has its limitations—it doesn't respond as well as a nicad to a high power draw, it discharges faster when not in use, and it can't be recharged as often. NiMH batteries can suffer from voltage depression like nicads, but by all accounts it's less severe. They sometimes need to be conditioned when they're new, charging and draining them a few times until they reach their peak capacity, and like nicad batteries they can be damaged by overheating, overcharging, or charging too fast.

Lithium ion batteries have more capacity than NiMH and nicads, handle high power demands just fine, take a lot of recharges, don't discharge when not in use, and are largely immune to voltage depression. They're also much lighter, so they're widely used in laptops. They have three downsides. First, they're much more expensive than nicad or NiMH batteries. Second, they have a limited life span (which some mistakenly call memory). As the battery ages it oxidizes internally, irreversibly increasing resistance so it's harder to get juice out of it. A lithium ion rechargeable commonly performs well for about two or three years, after which its ability to hold a charge drops markedly; exposure to heat—e.g., use in a hot laptop—will hasten its decline. If the one in your computer is four years old, you'll be lucky to get half as much time between recharges as when it was new. Finally, as most of the world now knows, lithium ion batteries have an occasional propensity to burst into flame, making it a matter of some importance not to doze through a conference call with your laptop on your lap.

Comments, questions? Take it up with Cecil on the Straight Dope Message Board, www.straightdope.com, or write him at the Chicago Reader, 11 E. Illinois, Chicago 60611. Cecil's most recent compendium of knowledge, Triumph of the Straight Dope, is available at bookstores everywhere.

 
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