Referring to FIGS. 14 and 15, a lithium battery circuit board 325 is mounted on the lithium battery connecting cover 304, and a lithium battery charging head 323 and a lithium battery output head 324 are welded to the lithium battery circuit board 325. A first mounting port 328 for mounting the lithium battery charging head 323 is formed in the lithium battery connecting cover 304, and the external device charges the lithium battery pack 3 through the lithium battery charging head 323 in the first mounting port 328. The lithium battery connecting cover 304 is provided with a second mounting port 329 for mounting the lithium battery output head 324, and the external device is charged through the lithium battery output head 324 in the second mounting port 329. Furthermore, the lithium battery circuit board 325 is fixed to the lithium battery connecting cover 304 through bolts, so that the lithium battery output head 324 and the lithium battery charging head 323 are fixed.