I need a power bank to charge my iPad Air 2 and iPhone 7 Plus on a trip to Eastern Europe this summer. I prefer one that is compact, has two ports and can charge both at the same time. Would the Anker PowerCore 15000 Redux be suitable? Or would something with less power also work? Anker has so many models on their website that my head is spinning. Is there really that much difference between 10000, 13000 or 15000? Thank you.