US Patent 9803609 System and methods for improved starting of combustion engines

This disclosure provides systems, methods and apparatus for a engine start system. In one aspect, the engine start system includes: a booster battery selectively connected in parallel with the primary batteries of the engine. The booster battery is disconnected when the battery voltage of the primary batteries is below a first target voltage. The booster battery is connected when the battery voltage of the primary batteries is at or above the second target voltage, or in response to an external input.