A battery assembly includes a protection member and a battery module including at least two batteries arranged side by side along a first direction and having a first outer surface and a second outer surface opposite to each other along a second direction. The protection member is in the form of a letter U with two vertical portions having different lengths, wherein a first protection section covers the end covers of batteries in the battery module, a part of a second protection section covers the first outer surface, and a third protection section abuts against an end cover of a battery corresponding to the second outer surface. The protection member can prevent the airflow, the flame and the like sprayed during thermal runaway, and control a thermal diffusion range during thermal runaway.