Scotty is correct on all points. The cig to USB handles the voltage change and isolates things nicely. I split the trunk 12v into 3 outlets, have 3 cig -to- USB converters installed powering iPhone, one Bluetooth transmitter as well as my TomTom. Clean, techno correct and easy to do.
BE VERY VERY CAREFUL when connecting ANYTHING directly to the battery!!!! Using existing outlets makes sure fusing is in place. This lowers the fire factor
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