I doubt they’d last anywhere near that long now.
The pantograph is lowered to allow for sequential re-energisation of trains when the OLE supply is restored.
If the supply has tripped due to a flashover on the roof of the train (usually due to tree branches or large birds) then the faulty train will be immediately identified when the pantograph is raised again.
When a Class 390 loses the OLE supply then the train auxiliary loads are supported by the train battery systems. Non-essential loads such as At-Seat Power Supplies are load shed immediately. Emergency ventilation is maintained for 60 minutes and reduced lighting will be maintained for at least 90 minutes (a mandatory requirement). In practice the lighting can be maintained for much longer, in one recent incident the circuits remained energised for over five hours.
Performance has improved in recent years due to the reduced load of LED lighting introduced during the refurbishment. In addition, the original vehicle batteries (in service for more than 20 years) are being replaced by new cells during the current Heavy Overhaul programme.
Drivers will sometimes be instructed to trip the train auxiliaries in order to limit discharge of the batteries to ensure the train can be re-started when the OLE is restored. However, in most cases this is not necessary.