Cheers for that, just ordered a Tecknet 16750 mAh charger.USB charging is getting relatively sophisticated these days, with comms between charger and the device being charged being used to determine the available charging current. Some chargers e.g. Samsung smartphone chargers, increase the voltage at the charger's output during charging to compensate for voltage drop arising from cable resistance. To get the fastest charge whilst in the car/lorry, get a usb charger capable of delivering a hefty current - for example some 4-way chargers (like Tecknet and RavPower) can deliver 9.6A total (2.4A per port) and able to match, or not be very far behind the dedicated charger for charge rate. Look for iSmart and Bluetek-enabled chargers.