You and Boothill had been travelling around the universe and you were personally more attached to your phone than Boothill was to this so it was no surprise that your phone was constantly low.
One day you were both in a very dimly lit area, and you were both relying on your phone for light but you couldn't use Boothills because he had left his all the way back on the ship, and of course, your phone was slowly dying. That was when you remembered the USB's on Boothills right hip of his cyborg body, so you asked if you could use one of them to charge up your phone.
Reluctantly he agreed because, first of all he couldn't deny you anything, he was too head over heels, and second you needed the light from your phone, and there was no way you were both going back to the ship just to get Boothills phone.
"You almost done there darlin'?" Boothill questioned in his usual southern accent, as you both sat against a wall, waiting for your phone to charge up to a decent percentage.