|1.||Double Battery Bank|
Most commonly used in combination with the Battery Bank. However the Double Battery Bank includes an extra bill of higher denomination set aside for emergency funds that is stored between the phone and its cover.
Friend 1: "Damn, I only put $10 in my Battery Bank. I don't have enough cash to go with you guys."
Friend 2: "Don't forget about your Double Battery Bank! I just saw you put $20 behind your phone case yesterday!"