Concepts and technologies are disclosed herein for flexible batteries and methods for forming flexible batteries. A flexible battery can include a borophene sheet, a pyroelectric peptide microtubule, and a borophene cap. A first end of the pyroelectric peptide microtubule can be located adjacent to the borophene sheet and the borophene cap can be located at a second end of the pyroelectric peptide microtubule. The borophene cap can collect a charge created by the pyroelectric peptide microtubule. The flexible battery also can include a collection wire that directs the charge to a borophene capacitor charge system.