You’re so busy on your phone or your laptop that you don’t notice it until it’s too late—the dreaded red battery symbol. Worse, you’re nowhere near an outlet, and you’re in the middle of an important project, or game, or text exchange. Time is running out. Suddenly you’re an action hero, attempting to pull just the right wire from the bomb that’s going to blow up the world!

OK, maybe you’re just trying to finish up that spreadsheet and send it to the boss before he comes in. But the point remains the same—you are in a race against time, and unlike the movies, you may very well not have enough time to do what you need to do. That’s why so many people have invested in portable power banks—easily transported high-capacity batteries that can keep your device charged up, and some can do much more than that. Here are three kinds of portable power banks and how they can help you.

This device weighs only 12.5 ounces but will charge a smartphone almost seven times before needing rejuvenated. Anker

Ever forget to recharge your phone? Or find out that the recharger wasn’t plugged in when you left your phone hooked up to it overnight? Or simply use your phone a lot one day, and don’t have time to sit down next to an outlet for an hour or two? Those instances are when a phone power bank will save you. These are small and lightweight, so they’re easy to pop into a pocket or backpack, and don’t cost a lot. Remember, the need for a phone power bank isn’t just for convenience—it can also be for safety. If you’re traveling and run out of power (and especially if you’re overseas, where the power outlets are different from those in the U.S.), you want to make sure you’re able to stay in touch with fellow travelers, contact authorities if necessary, and reach out to emergency contacts at home.

Some portable battery can store enough juice to power a small laptop computer. Anker

Having your laptop run out of power can be anything from a nuisance to a career risk. Many of us use laptops to do work away from home, and they’re great for working on trains and planes, at parks and waiting areas. But if you run out of juice, your laptop becomes totally useless. That’s when a power bank designed to recharge a laptop can save the day. Such power banks can also recharge your phone simultaneously—a wonderful benefit if you’ve ever found yourself in the Stone Age-like position of having both your cell and your laptop die at the same time.

A large capacity power bank can recharge smartphones and laptops, or provide roadside assistance in an emergency. Halo

If you spend a lot of time in your vehicle—and especially if you need it for your job, or if you live in a remote area—consider one of these. A power bank that will charge up your phone and laptop, and also jump-start your car or truck if need be, can save you time, money, and keep you safe. Being stranded in a vehicle far away from any services, with your phone running out of power, isn’t just an inconvenience—it’s dangerous. That’s when a power bank can literally save your life. Consider a power bank that will jump-start a car if you’re going to be taking a long vehicle trip through uninhabited areas, on an extended camping trip, or if you leave a vehicle for long periods somewhere and want to make sure you can get it started when you return.