Newegg offers the refurbished Digital2 4,400mAh Portable Battery in Metallic Purple, model no. RP-4400F_MPL, for $11. This $11 mail-in rebate cuts it to $0. With $1.99 for shipping, that's tied with our mention from a week ago and $15 under the lowest total price we could find for a new unit. It includes a microUSB to USB cable and features an LED battery status indicator. Deal ends October 5.
A 90-day warranty applies, but it is unclear who backs it.