As one of its daily deals, Best Buy offers the Mophie 4,000mAh Juice Pack Powerstation in Red, model no. 38205BBR, or Purple, model no. 42673BCW, for $14.99 with free shipping. That's the lowest total price we could find by $7. The Mophie Juice Pack Powerstation is an external battery that works with USB-based mobile devices and smartphones. Deal ends today.