This is the first in a series of travel technology stories developed by, the independent guide to technology, for

Cell phones, tablets, and other mobile gadgets have made the dull parts of traveling a lot more bearable, especially for families with kids on long car, train, or plane trips. Unfortunately, the batteries in those gadgets can't keep up with us.

The best solution is to pick up a backup battery. Many add-on batteries will work with any phone, tablet, MP3 player, or portable gaming system?even with multiple gadgets. Backup batteries come in many different sizes, but they're all measured in milliamp hours, or mAh. Your phone or tablet's battery is measured in mAh, too?pull it out (if you can) and take a look. You can expect a backup battery to boost your device's life by as much as you'd expect from the mAh stored, minus about 20 percent for inefficiencies. So if you have a 1,500mAh battery in your phone, a 4,000mAh backup battery should give you more than two full charges.

You have to balance size, convenience, and charging time. Small batteries are very portable and flexible, and also hold about one charge for most smartphones. Bigger batteries take longer to charge, and they usually require you to tote around a USB cable, but they're a lot more capacious than the little guys. has reviewed a wide range of backup batteries, so you're sure to find one that fits your needs below, from a tiny iPhone juice booster to beefy tablet refillers.

If you have an iPhone 4 or 4S, these iPhone battery cases could be a better bet.

Add-On Batteries Included in This Roundup

Energizer XP4001

XPal Power makes a wide range of backup batteries under the Energizer name. The XP4001 is the best bet for recharging most phones and tablets. While we prefer the Sanyo eneloop Mobile Booster overall, the XP4001 is less expensive and can charge some higher-drain devices than the Sanyo. Read the full review ››

Mophie Juice Pack Boost

Made for iPhones and iPads?and nothing else?the Mophie Juice Pack Boost is a handy little extra battery which can give your iDevice a bit more charge. While it's slim, well-designed, and has more than double the capacity of the Juice Pack Reserve, there are much more flexible options out there. Read the full review ››

Mophie Juice Pack Powerstation

The $80 Mophie Juice Pack Powerstation gives you less battery life than competing products at the same price point, but it's a lot prettier. Whether that's worth it is up to you. Read the full review ››

Mophie Juice Pack Powerstation Pro

Extreme travelers will appreciate the rugged design of the Juice Pack Powerstation Pro, whose 6,000mAh battery can resist rain, sun, and dusty conditions. More casual voyagers may not find this worth the extra price. Read the full review ››

Mophie Juice Pack Reserve

The teeniest battery in Mophie's backup line could easily be mistaken for a cigarette lighter. It's designed primarily to give a quick burst of power to iPhones, with its tiny 700mAh capacity and built-in 30-pin Apple connector. Read the full review ››

Sanyo Eneloop Mobile Booster KBC-L2S

Our Editors' Choice for backup batteries, the Eneloop Mobile Booster offers the best balance between power, price, and portability, fitting 5,000mAh of juice into a petite 4.6-ounce white body. You'll find it costs much less than $80 at retail, too. Read the full review ››

Scosche FlipCharge Burst

Aside from the unfortunate name (I'd like my battery to neither scorch or burst, thanks) the iPhone-exclusive FlipCharge Burst is a little expensive for the limited 720mAh of juice it can provide. But it's very flexible and easy to use, thanks to a built-in 30-pin Apple connector and a USB charging cable. Read the full review ››

Tylt Energi

The Tylt Energi is a very convenient way to charge up any phone or tablet with a USB or MicroUSB port. We love its built-in AC power plug and MicroUSB tail. But although the size, price, and options are on target, our ideal backup battery holds a bit more energy. Read the full review ››

Zagg ZaggSparq 2.0

Need a lot of power to charge your phone or tablet? Zagg's ZaggSparq 2.0 is a powerful, elegant, and, at $99, pretty costly portable battery that can run an iPad all day long. There's one big caveat, though: You may need to go through a few units before you find one that works. Read the full review ››