Santok offers this in-car charger splitter (model: CARSPL2USBxx) that comes with two USB ports for charging. The device basically converts regular cigarette lighter socket into two 12V sockets. It comes with an arm that can be angled to the most convenient position and also has a replaceable fuse as an extra safety feature. Check out the product page.
Santok In-Car Charger Splitter with two USB ports
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