Walmart offers the Ozark Trail 2,400mAh Portable Phone Charger with Solar Panel for $12. Opt for in-store pickup to dodge the $5.99 shipping fee. That's $17 under our mention from a year ago and the lowest price we've seen. (It's a current low by $9.) It features a 2,400mAh rechargeable battery and eight hour charging time with the solar panel.