Long battery life is probably the most important feature for a smartphone. After all, once your battery is dead, that expensive handset is just another hunk of plastic and metal. With Motorola's new Droid Maxx, you'll rarely worry about your device running out of battery power. Offering nearly 10 hours of juice, this is the second-longest-lasting smartphone we've ever tested. See whether this handset is worth the $299 asking price.