Also, if you have that exact model car charger, the charger is almost certainly the issue. Most non-Apple devices expect the data lines to be shorted together to signify that it is not a data USB port (which has a maximum current of 500mA) and can put out extra amperage. This charger does not have that, because Apple-specific chargers use a resistor across the data lines instead which does not register as a short for other devices.

Read the reviews.

If you don't plan on plugging in other USB devices, I recommend a dedicated charger. If you do plan on plugging in other devices, I recommend one that specifically says Android tablets so you know that it will work properly with the S5.

I am still confused as to how this charger which runs at 20W power can completely drain the car battery in half an hour. Am I missing something?