Mophie's gear rarely drops in price outside of major sale events. This battery rarely goes below $40 but has dropped to $15 today only. It has 2 USB ports and a 6000mAh capacity. It sold out super quickly last time it hit this price.
Did you invest in a fancy Apple iPhone, Airpods, and an Apple Watch? Mophie's charging pad is one of the only ways to wirelessly charge all three of them at once. Even works through cases up to 3mm thick.