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

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

1. Is Zero Voltage of Single Battery?

2. Plug short circuit, break circuit, bad connection with plug

3. Lead and battery de-welding, virtual welding

4. Battery internal connection errors, leak welding between connecting sheet and battery, virtual welding, de-welding, etc.

5. Battery internal electronic components are incorrectly connected and damaged