One thing I thought of afterwards was that two cells are about 6 to 7 volts right?
You might want to invest in a buck converter that will change it to 5 volts for you.
I did it with mine. They change the 24 volts to 12 for my heated seat and another one to 5 volts for all of my usb accessories.?
Just an idea.
Hope it works out for you.