Various embodiments of a battery assembly include a first housing shell, a second housing shell, an insulator and battery components. The first housing shell has a first perimeter side wall, a first housing bottom, and a first contact area on the first housing bottom. The second housing shell has a second perimeter side wall, a second housing bottom, and a second contact area on the second housing bottom. The second housing shell is disposed in the first housing shell with the second contact area opposing the first contact area. The insulator is interposed between the first housing shell and the second housing shell to effect electrical insulation between the first housing shell and the second housing shell. The battery components include an anode electrode, a cathode electrode, and a separator interposed between the cathode electrode and the anode electrode. The separator contains an electrolyte.