Tanga offers the ReadyCharge Go! 3,000mAh USB Portable Battery Pack 4-Pack with Charging Base for $29.99 with free shipping. That's tied with our mention from two weeks ago and the lowest price we could find by $3. Each power bank features a 2.1-amp USB charging port and an LED flashlight. It includes two 8" microUSB cables, two 8" Lightning cables, and a charge dock that can hold and charge all four battery packs simultaneously.