An internal combustion engine includes an engine block including a cylinder, a piston positioned within the cylinder, a crankshaft configured to be driven by the piston, a fuel system for supplying an air-fuel mixture to the cylinder, a starter motor, and a lithium-ion battery mounted on the engine, the lithium-ion battery configured to power the starter motor to start the engine, wherein the piston is configured to reciprocate in the cylinder along a cylinder axis, wherein the lithium-ion battery includes at least one lithium-ion cell having a longitudinal cell axis, and wherein the cylinder axis and the longitudinal cell axis are not parallel to one another.