Battery pack for driving electric motor of compact engine starting device, engine starting device driven by the battery pack, and manual working machine having the engine starting device

It is an object of the invention to a battery mounted in a working machine in which a compact electric motor (131) for starting a compact engine can be driven smoothly and safely for a long term, and the battery is reduced in size and weight to the utmost. Batteries are packaged as a battery pack (16). A lithium-based secondary battery includes two cell is incorporated in the battery pack. The entire discharge capacity of the cells is 500 to 2000 mAh, and discharge voltage per one cell is 3.0 to 4.2 V. Various electronic circuits a driving circuit and a battery protection circuit and a start switch relay circuit of an electric motor (131) connected to the battery and incorporated in the battery pack are also incorporated in the battery pack (16). Maximum discharge current of the battery has high rate of 10 to 60 A. The protection circuit includes a special overdischarge inhibit circuit (A) which is interposed at least in the electric motor driving circuit and which automatically stops the driving operation of the electric motor (131) after time required for starting the engine (10) elapsed. The volume of the battery pack (16) is as extremely low as 2.5 × 10 4 to 1.0 × 10 5 mm 3 . Since high current can flow, the time required until the engine (10) is started from the actuation of the electric motor (131) can be set to an interval as short as 5 to 15 seconds.