What if your battery can't be removed, as in Apple's latest laptops? Buchmann says that new laptop designs often place batteries in cooler parts of the machine, and they may also include some intelligence to limit the stress of a fully-charged battery—that is, the machines stop applying a charge when the batteries are just under full capacity. This prolongs the battery's lifespan. The trouble is, most laptop manufacturers keep their charging algorithms secret, so it's not possible to know which laptops use this battery-prolonging technique. (Bachmann assumes that Apple does so based on its battery-promoting advertisements.) But even if your computer is clever enough to stop charging the battery when it's full, you're still better off removing the battery if it is removable. This will help your battery beat the heat.
Phones, cameras, and other gadgets: In general, the rules are the same as for laptops: Keep the battery in the 20 percent to 80 percent range, and keep it cool. If you leave your phone on a hot car seat all afternoon, or if you run down your camera at an all-day trip to the zoo and then forget it in a sock drawer for six months—well, somewhere a little battery angel loses its wings.
The best way to store batteries that you won't be using for a long time—as in a camera, though this also applies to laptop batteries—is to charge them to the 40 percent level first, Bachmann says. Batteries "self deplete"—meaning they lose power even if they're not in use. Charging the battery a little bit before you put it away ensures that it doesn't get down to dangerously low levels while in storage.
The memory effect: Will your battery lose capacity if you don't let it go down to zero every once in a while? Not likely. The memory effect applies only to nickel-cadmium batteries, whereas most modern electronics use lithium-ion or the more advanced lithium-ion polymer. Not only are lithium batteries immune to the memory effect, they also don't require you to do anything special the first time you use them (like charge them up for 24 hours, as some gadget manuals say). Nicad batteries are still found in cordless phones, electric toothbrushes, and other cheap gadgets, but they're usually pretty inexpensive to replace.
How come my battery gauge is off? Making an accurate battery gauge is much more difficult than measuring how much gas you've got in your car. Since a battery's capacity is constantly decreasing, your gauge will likely get less accurate the longer you own your gadget. The length of a charge also depends on impossible-to-predict environmental factors like temperature. "The technology to measure batteries is just not that good," Buchmann says. "We can't do it. It's that simple."
Most battery meters in electronics work by monitoring electrical inflows and outflows—in other words, how long you charge and how long you use your device. They also try to guess how your battery may have become degraded over time. But each time the computer makes such a guess, it adds errors into the calculation. These errors build up over time, and eventually you notice your laptop dying even though the battery meter says you've got 40 minutes left.
To solve this, you should occasionally "calibrate" your charge meter by depleting your battery completely, then charging it up fully. This usually resets your machine's "flag" for your battery's capacity. Of course, running it down and then charging it up again puts more stress on your battery, accelerating its death. But there's no getting around that.