The Ultrapak comes in two sizes. The large one sells for $100.

The Ultrapak comes in two sizes. The large one sells for $100.

Say you've got 15 minutes in an airport between flights and your phone is nearly dead. What do you do?

In the past, you had two choices. You could give it the old college try: find an outlet and plug in your phone, watch the battery meter inch up as the minutes run down, and pray that you've gained enough power to get you through your day. Or you admit defeat and let your phone die. In 15 minutes of charging, you're only going to get a few percent more battery power anyway.

What's the point?

But over the last few weeks I've been testing a remarkable third option, a device that lets you fully charge your phone in just 15 minutes. Well, sort of.

The device is an Ultrapak battery pack, an external charger made by a firm called Unu Electronics. External battery packs aren't novel. These little devices are essentially just batteries in a case — you charge it up by plugging it into the wall, then plug your phone in to suck up the power stored in the pack.

But the Ultrapak does something unusual among battery packs. It quickly sucks up power, about eight times faster than other battery packs, the firm says. It's so fast that, in about 15 minutes of charging, the pack gets enough juice to charge a standard smartphone one time.

In other words, if you've got just 15 minutes to charge your device, you should plug the Ultrapak into the wall instead of your phone. The Ultrapak will rapidly ingest power. Then, when you get on the plane, plug your phone into the Ultrapak. Over the next couple hours, your phone will slowly sip the power in the Ultrapak, eventually getting to 100 percent.

It really works. I use my iPhone a lot, and I frequently find myself between meetings — in coffee shops, airports — with just a few minutes to power up. In those instances the Ultrapak, which I keep stuffed in my work bag, has become a lifesaver, the best way to charge up very quickly.

The Ultrapak comes in two sizes. The large one, which sells for $100, is about the size of a men's wallet and weighs about 10 ounces. When fully charged, which takes about an hour and a half, it has enough power to charge up a phone about four times (or a tablet one time).

The smaller one, which sells for $60, is about half the size and a carries a third of the battery capacity. Both units ingest power at the same rate—in about 15 minutes, they'll get enough power to charge your phone one time. If there's a better way to power up quickly, I haven't seen it.