Amazon has the AUKEY Slimline 10,000mAh Battery Pack on sale right now for just $12.87. That is down about $10 from its original price, though you do need to use the promo code 73YLYYV3 at checkout to get that price. This brings this particular battery pack down to its all-time lowest price, which makes this an impulse buy.
The AUKEY Slimline 10,000mAh Battery Pack is a great battery pack to pick up and stick in your backpack, since it is a slim design battery pack and has a decent capacity as well. It's a 10,000mAh capacity here, so you're going to get about three full charges here - depending on your smartphone. Now, this particular battery pack does not sport Quick Charge 2.0 or 3.0, unfortunately. But it does output at up to 2.4A. That is about the same speed as Qualcomm's Quick Charge 2.0, but it is not technically the same. So you'll still get some fast charging here, just not as fast as some other battery packs out there. The main selling point here is the slim-ness of this battery pack. Seeing as most battery packs are looking to add as much capacity as possible, AUKEY has made sure that this one is pretty slim, and can even fit in your pocket, if you wish to do so.
This item is also eligible for Amazon Prime's free shipping. Which includes free two-day shipping, and pretty cheap (usually $3.99) next-day shipping if you need it extra fast. If you are not an Amazon Prime member yet, you can sign up for a free trial of Amazon Prime. You'll get 30 days free (if you're a student, you get 6 months), and then it's $119/year (or $59/year for students). Prime members do get a whole lot more than just free shipping though, so be sure to check out the full benefits.