A spec you’ll often see is mAh, which stands for milliamps hour. The mAh spec is a measurement of power over time—the higher the mAh the more power the battery contains. To fully charge a phone you’ll need 3,000 to 5,000 mAh. There is a big price jump between 10,000mAh and 20,000mAh power banks for camping, so if you’re not sure which one you want to buy, it’s good to consider what your needs are first. Typically, a 10,000mAh battery size will provide enough juice for a couple of phone charges. If you’re heading out for a weekend—and you aren’t planning to watch a movie on your iPad—this is likely sufficient. If you’re heading somewhere out of cellphone range, one way to increase your battery life is to check that your phone is switched to airplane mode.