Ending today, Groupon offers the Unu Enerpak Tube 5,000mAh USB External Battery Pack in White (pictured) or Black for $29.99 with free shipping. That's the lowest total price we could find by $5, although we saw it for $3 less in March. It features an ability to extend up to 15 hours of talk time, built-in flashlight, and more. Note that no AC adapter and no cables are included, but it's purportedly compatibile with "all" USB chargers and cables that come with cell phones and tablets.