If you’ve ever been out and about for an extended period of time, you probably know the pain of watching your iPhone’s battery die before your eyes. 20%… 15%… 5%. If you’re regularly finding yourself in the red zone, you may want to check out the Powerbag Sling pack.

Before we talk about the built-in battery, lets go over the actual bag itself. While Powerbag doesn’t design these bags in-house, they’re designed by FUL, a well-known backpack maker. In fact, the Powerbag Sling is completely FUL branded, except for one Powerbag logo on the arm strap and in the pocket where the battery resides.

The Sling features a padded laptop compartment as well as a tablet compartment which fits my iPad 2 perfectly (with or without a Smart Cover). This bag also features an extra gadget pocket which houses the removable 3000mAh battery as well as a mobile phone, MP3 player or handheld video game player. I’m able to fit my iPhone 4S and Nintendo 3DS into this pocket at the same time – but there’s not quite enough room for the PS Vita as well.

Additionally, this backpack has a small quick-grab pocket which is located on the right-hand side of the backpack. Usually I store spare flash drives and SD cards in this pocket for easy access.

Finally, the battery which is built into the Powerbag has a maximum capacity of 3000 mAh, with which you’re able to charge the average smartphone two times. If you’re in need of additional battery capacity, you can buy extra 6000 mAh and 9000 mAh batteries on Powerbag’s website. You can easily check the charge of your battery by pressing the power button which is located on the front of the bag.

Now you’re probably wondering: “Can I charge my iOS devices in this bag?”. The answer is a simple yes – The Powerbag Sling features an Apple 30-pin dock connector as well as micro and mini USB cables to charge your iPhone or iPod touch. They also give you an extra USB port which allows you to charge high-powered tablets such as the iPad and Samsung Galaxy Tab with the bag.

Overall, I was really impressed with the Powerbag Sling because of it’s over-the-shoulder comfort and easy access to the stowed gadgets. While the price is rather steep at $139.99, I think it’s definitely worth it for anyone who needs to constantly charge their gadgets on-the-go. Already, this bag has saved me on multiple occasions when I needed an extra battery boost but couldn’t get to a power outlet to charge up the ‘traditional’ way.

If you’d like to buy the Powerbag Sling for yourself, head over to Powerbag’s website. This pack is currently available in six colors and retails for $139.99.

Disclosure: Powerbag kindly sent out this review unit free of charge.