Now I am asking whats the most efficient engine temperature for horsepower, but I assume that the best temperature is also the most efficient (as for gas mileage). If there are two different answers please list them both.
...via a USB cable? I recently bought a new cellphone and it came with a standard power outlet charger, and a USB cable. I'm able to charge my phone using either one, but I'm wondering if one of them is more efficient than the other.