I have 3 generations of flip phones, from a old nokia to a Sony Ericsson w580i. They all eject their battery upon impact. Considering it wouldn't be difficult

I have 3 generations of flip phones, from a old nokia to a Sony Ericsson w580i. They all eject their battery upon impact. Considering it wouldn't be difficult at all for the battery cover be more tight, or have something that clips on, it's probably accurate to describe it as an engineering decision.