You probably plug in your smartphone every chance you get.

After all, why take chances? You want to hit the street with 100 percent battery life, and the little number up in the upper-right corner of your phone says that you’re only at 80 percent.

Unfortunately, you might be doing more harm than good. Smartphone battery indicators aren’t perfectly reliable, thanks to a little-known secret of battery engineering, and when you charge to 100 percent, you’ve actually got less battery life than you think.

Modern devices use lithium-ion batteries, which can charge relatively quickly.

Of course, there’s a catch: Lithium-ion batteries are prone to overheating, which can potentially set off a dangerous chain reaction. The battery can even explode, although the far more likely outcome is a gradual loss of power.

Most lithium-ion batteries slowly wear down with each full charge after about 300-500 power cycles. That’s why your phone battery doesn’t seem to last as long after a year or two of use—it’s not lasting as long because the battery has degraded.

Fortunately, smartphone manufacturers can minimize the effects of overcharging by using a few clever tricks.

First, they only “fast charge” a battery up to about 80 percent of its total capacity. Past that point, the smartphones switch to a “trickle charge,” which slowly charges the battery to prevent an excessive load.

If battery indicators were perfectly accurate, smartphone users could see the trickle charge, and they’d be outraged since their $70 phones would be charging so slowly. To prevent hordes of angry customers from storming their offices, smartphone manufacturers came up with another trick.

That’s why your smartphone’s battery indicator is wildly misleading.

It continues to add percentage points, then holds steady at 100 percent. Meanwhile, your phone’s actual percentage is substantially lower. When you’ve got a real “full charge,” your battery indicator might read 90-95 percent or so.

But before you start writing angry letters to your smartphone manufacturer, consider the benefits. By cutting the electrical current before reaching an actual 100 percent charge, your smartphone drastically extends its battery life, allowing about 1,200 to 1,500 cycles before degradation.

If you want your phone to last as long as possible, don’t charge all the way every time.

You’ll extend the battery life by keeping the battery indicator in the 40-80 percent range. Charge frequently, and prevent the battery from completely discharging. Don’t charge your phone in an extremely hot or cold place, and always use a high-quality charger that’s specifically designed for your device. Of course, some of these tips aren’t practical all the time; if you’re going on a flight, for instance, you might feel more comfortable with a 100 percent charge, and you’re not really doing too much damage. Just don’t rely too heavily on that battery indicator, and don’t assume that your phone needs to stay fully charged to function.

Manufacturers regularly introduce new lithium-ion batteries that improve on existing battery technology, but in the meantime, smart charging practices can help you get the most out of your electronics.