Apparently most of these events were due to excessive discharge while on a ground. [...] This is not a safty issue.
As far as I understood, excessive scharge will make the cells instable and lead to thermal runaway. With that respect, discharge
is a safety issue. However, it seems to be perfectly prevented by the integrated logic, switching off the battery and making it unserviceable if it is discharged below a defined (still safe) threshold. So the overall Boeing design for this aspect worked perfectly for safety, but is a nightmare for maintenance cost / unscheduled removal.