 Battery anxiety is a real thing. When it's only 3 p.m. in the afternoon and your iPhone's down to 10% battery left, wondering if that's gonna make it through the rest of the day can really make you sweat. The iPhone 6 doesn't let you swap out batteries when it dies, but not all hope is lost. You just need a case that provides extra battery life and protection when you need it. You may have heard people refer to these cases as Mophies, and that's because Mophie was the first brand to really make them popular. But now there are a ton of different options available for the iPhone, and if you want the best option for your iPhone 6, we recommend the Incipio Off-Grid Express. It's got lots of battery capacity, so you can charge your phone completely from dead and then some. It's slimmer and lighter than competitors, and it's easy to remove from your phone when you don't need the extra bulk or battery. It's also less expensive than some of the other cases we tested. Here's how virtually all of these battery cases work. You slide or snap your iPhone into the case, which will then have a button or switch to turn on its battery feature. Once you turn it on, the case's battery will then recharge your iPhone's battery. The Off-Grid Express can recharge the iPhone 6's battery from zero to full, and then a little more. For most people, that means being able to go up to two days away from a power outlet. Once the Off-Grid is depleted, you plug it in just like you would your phone to charge it back up. The advantages of a battery case like the Off-Grid Express are pretty obvious. You don't have to stop to plug in your phone to an outlet. You don't even have to stop what you're doing, just flick the case on when your battery is low and keep on going like you normally would. And since it's a case, it can protect your phone from damage at the same time. Some cases, like the UNU DX6, have cutouts for the volume rockers and power buttons that can make it hard to reach those buttons. But our choice uses pass-through buttons that are much easier to activate, especially if you have large fingers or gloves on. Remember that Mophie I mentioned earlier? Mophie does make a few cases for the iPhone 6, and they're actually quite nice. They hit all the marks we're looking for. Large battery capacity, nice buttons, ease of removal. They're also really well built, kind of like the Cadillac of battery cases. But they're also priced like a Cadillac, and the Mophie Juice Pack Plus for the iPhone 6 that we tested is considerably more expensive than the Incipio, without offering a significantly different experience. Now there are some annoyances when you're using a battery case. The most obvious one is that it makes your iPhone a lot thicker and considerably heavier. Options like the Boost Case make your phone more than twice as thick as it would be without the case. But a good case, like our pick, lets you take your phone out easily, so you only need to bulk up when you're actively charging your phone or know that you won't be near an outlet for a long time. There are other options, like Otterbox's Resurgence, which provides a lot of protection from drops and damage, but it's really hard to remove from your phone. The other annoying part is that every battery case on the market covers up the iPhone's headphone jack and lightning port. For your headphones, the cases provide a pass-through, and most will accept Apple's standard earpods with it. But if you're using a different set of headphones, you'll likely have to use an adapter, which comes supplied with every case we looked at. Or you could just go wireless with Bluetooth headphones and avoid the issue entirely. For charging and syncing with your computer, you'll have to use a micro-USB cable with most cases, meaning your stash of lightning cables won't do much good anymore. Getting stranded with a dead iPhone can not only be annoying, it can be a legitimate safety concern. But with a battery case like Incipio's Off-Grid Express, you don't have to worry about being away from a wall outlet all day long.