A Battery Assembly comprises a rack assembly, a plurality of guiding strips, two polar heads, a plurality of lithium batteries and safety units. The guiding strips are connected to the polar heads and are disposed on the rack assembly, respectively. The rack assembly has a containing space for accommodating the lithium batteries, and each lithium battery is connected to the guiding strip by a guiding piece via one safety unit, such that the lithium batteries are connected in parallel, thus providing enough power with a small size. In addition, each safety unit can cut off the broken lithium battery separately, so as to avoid the immediate shut-off of the electric power.