This is a question related to What makes primary batteries leak on very deep discharge?
What are the dangers of deep discharging a cell or battery? I've seen a LiPo battery getting puffy most likely because of deep discharge, so I'm curious if there are safe cells. E.g. does a 0 V NiMh cell pose a danger? I'm aware that you most likely destroy your secondary cell by discharging it really deeply.
Are there safe or unsafe battery or cell technologies, either primary or secondary, in respect of deep discharging? Can a circuit without battery protection mechanisms like a joule thief make cells pop, heat, or burn?