Amazon has a great deal on the “AUKEY 12000mAh Portable Charger”. I used a variation of this charger during my trip to Australia last month and it worked great.
It lists as costing $25.99 but check out this screenshot:
To get the deal, click on the drop-down menu where it says, “3 Applicable Promotion(s)”. Click on the bottom one where it says, “Save 54% each on AUKEY 12000mAh Portable Charger offered by Aukey Direct when you purchase 1 or more”. At checkout, you’ll see the price change to $12!