PowerGen via Amazon offers Prime members the PowerGen Dual USB 3.1-amp 15-watt Car Charger in White, model no. PGCHCAR36A, for $7.99 with free shipping. (Non-members can spend $25 or more to receive free shipping; otherwise it adds $4.99.) That's a buck under the lowest total price we could find for a similar 3.1-amp, 15-watt car charger sold elsewhere, although we saw a similar item for $3 less in June. This charger is compatible with a range of USB devices and features two ports. Note that a USB cable is required but not included.