Definitely recommend Anker.
Their well priced, and useful for so many applications, even providing instant charge for a mobile phone, and a digital camera, instant recharge power, anywhere, even in the middle of the Carneddau.
Used it recently, when the battery of my friends I Phone 10 went too low for comfort.
The model i have, is the Astro E1, which according to the website, has enough internal power to recharge two Apple I Pads from cold, which is serious power from something so portable.
It currently costs £13.99 from Amazon, and it arrives in its own rather nice carrying pouch.
You may want something a little more powerful, but i recon the Astro E1 would be more than adequate for your requirements.