Daily Steals via eBay offers the Lenmar ChugPlug External Power-Supply Pack for MacBook Air or Pro for $44.99 with free shipping. This $155 off the original price, $30 better than Amazon, $4 less than our previous mention and the best current price. Rated 3.8/5 stars.
Lenmar’s ChugPlug can add up to four extra hours of battery life to a 11-inch MacBook Air or up to three hours to the 13-inch MacBook Air/Pro. Even though it cannot supply a full charge, it is enough to get by until you reach an outlet. It is compatible with standard 45 and 60W Apple MagSafe Power Adapters. Note: not compatible with 15-inch MacBooks. The ChugPlug was one of our top portable battery options for MacBooks.
It ships with a one-year manufacturer warranty.