Let’s cut to the chase: BatteryBox ($220) doesn’t charge your MacBook, it powers it. What does that mean? Say your MacBook is at 76% charge. If you plug it into a BatteryBox, said BatteryBox will keep your MacBook at 76% charge, bypassing the battery. The fewer cycles your battery goes through, the less wear and tear it gets.
Oh, and the other key details: BatteryBox can power a MacBook Air for thirteen hours straight or charge an iPhone eleven times. That’s a lot of power.