Amazon offers Prime members the Nyko Charge Base 360 S for Xbox 360 for $14.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping adds $4.98.) That's $2 under our mention from a year ago and the lowest total price we've seen. (It's a current low by $5.) It includes two rechargeable batteries with up to 25 hours of playtime each, stores two Xbox 360 controllers, and can charge via USB or AC power.