If you've been waiting for a reason to pick up a big external battery, perhaps you should consider today's deal as a potential motivation. Right now we've got a coupon code that brings Anker's PowerCore II down to $34 over at Amazon. Not a bad price for something with a 20,000 mAh capacity that can charge over a pair of inputs at 4A, and spit 6A combined over three USB ports, with 3A max output per port.
This deal requires that you enter coupon code LIPO3399 during checkout. So, if you don't see that the price has dropped, remember that you won't see the price decrease until you have entered the code just before you place your order. Also, keep in mind you might have to pay for shipping if you aren't a member of Amazon Prime.
The battery is a pretty decent size, although the method of charging to be able to pull the full 4A in is a bit strange. It uses a pair of micro USB ports that have to be used in conjunction with a compatible power source in order charge at full speed. I guess it's nice that Anker included a faster charging method since big batteries do take a while to fill up. It may be a bit awkward with two cables when trying to fill it up, though. Keep in mind that it only comes with the battery, a pair of USB cables, and a carrying pouch. So, if you don't have a charger that can spit 2x2A, perhaps you can put the $10 you are saving towards one of those. If you like coordinating brands, I hear Anker makes a decent one of those, too.