What are the possible reasons for zero voltage or low voltage of the battery pack?

What are the possible reasons for zero voltage or low voltage of the battery pack?
> Single battery in the battery pack is zero voltage.
> Short circuit or open circuit of the connector or wrong connection.
> Desoldering or cold solder joint between the batteries and lead.
> Wrong connection between the batteries. There is desoldering or cold solder joint between the connection strap and battery.
> The wrong connection or failure of the electronic components inside the battery pack.