A fabrication method of a battery includes the steps of providing an electrode group, a first sealing film and a second sealing film; bonding a part of a first surface of the first sealing film and a part of a first surface of the second sealing film by thermo-compression to form a sealed chamber, wherein at least one of the first sealing film and the second sealing film has a redundant part located outside the sealed chamber and without being bound by thermo-compression, and a part of the electrode group is disposed in the sealed chamber; and injecting an electrolyte into the sealed chamber.