HyperJuice 2 100wH external battery – $299
As I mentioned in my previous pick, batteries are a fact of life. Since Apple began building notebooks with non-removable batteries, an external battery can really save the day. So, in addition to small and light external battery for your iPhone or iPad (like the aforementioned JackeryAir and RAVpower models) a larger battery pack has the advantage of being able to charge your MacBook.
Sanho's HyperJuice batteries are my favorite large-format external batteries and the HyperJuice 2 ($249) is the top of the line. It's a 100Wh/27,000mAh pack that charges all MacBooks (including Retina) and comes equipped with dual 12w (5V/2.4A max) USB ports which can charge two iPads simultaneously at maximum speed. And since they're USB power outlets they can charge almost any gadget, provided that you have the cable.
HyperJuice 2 has a slick OLED display that displays the battery percentage, temperature and remaining charge time, which is extremely handy to know. The industrial grade Lithium-Ion cells are rated for up to 1,000 charge cycles and are replaceable when they reach the end of their useful life.
The secret sauce is the Magic Box, a $50 companion accessory that allows you to convert your MacBook's MagSafe AC adapter to work with the HyperJuice 2. After a 5 minute conversion, the HyperJuice 2 can charge your MacBook (including Retina models) and an included adapter allows you to charge your MacBook from your vehicle's 12 volt power outlet.
The battery itself costs $299, or $349 with the Magic Box DIY conversion kit. For $399 Sanho bundles a pre-modified MagSafe adapter and Magic Box adapter. Each of the HyperJuice 2 models is $50 for Cyber Week ($249, $299 or $349), which ends on Monday, December 9, 2013. I can't emphasize enough how important a good backup battery is, mine paid huge dividends during hurricane Sandy last year and I bring a battery or two when we go camping in the summer.