PedalCell can charge nearly any USB battery pack. For the best experience, we recommend that riders use batteries with 'pass-through' charging, the ability to use the battery while it's being charged. We wrote a blog post on the pros and cons of pass-through batteries here.
Here are a few other tips:
1) We recommend you keep the battery size <= 10,000mah if possible. Larger batteries can be less efficient and get quite bulky.2) Battery should accept a 3A, 5V charging input for maximum charge speed with PedalCell