Should I switch off during a power cut?

After Storm Darroch in Dec 2024 we had a 36-hour power cut, and after that the battery would neither charge or discharge. The green light in the middle of the display on the inverter was flashing. Last week an engineer finally arrived and gave it a "jump-start" with a powerful charger and after 15 mins all was working perfectly again (apart from a hiccup that night.)
He said the problem was that the battery voltage had fallen below 50V, even though the battery capacity showed 5%, and that it therefore could not respond to calls from the inverter. He advised switching off the battery during power cuts (we don't have the ability to supply power to the house when the grid is down).
So, what should I do during a power cut? Switch off the battery or switch off the whole PV array-inverter-battery installation. I would greatly appreciate any advice a wiser head could give.
[Details: 14 PV panels, Inverter GIV-HY 5.0, Battery Giv Bat 5.2. I should mention that during the outage, we had a period of about 30min at reduced power which might have confused the system.]

I guess turn the whole thing off if the battery gets down to say 30% unless the sun is shining and assuming it's a hybrid inverter - it'll still charge.

When the sun goes down, if the battery is less than 30% turn it all off as per the installation guides - can't remember the order, but you've got the AC connection, the PV connection, the battery breaker and the battery itself.

Thank you, TX200, that was most helpful. The battery was at 22% when the problem started and down to 5 % when it was jump started.
I keep the power down sequence next to the gear just in case ... Fingers crossed1

Hmmm this really shouldn't be necessary the battery should cope with 36 hours at 5%.

Was the battery in a very cold location?

Was it really 5% though? The SoC might not be 100% accurate. Or should that say might not be 5% accurate. 🤣

Thanks for your comments guys.
The setup is in the garage where the CH boiler lives, so quite warm, and looking at the past records never went below 14 deg C. I don't know how charge is estimated, possibly a look-up table of charge v voltage. I did try a scatter graph of charge v voltage, but it's not convincing.
The installer who fixed it said I should have turned the battery off to save it, but as M_J says I would have thought the battery should cope with that.
It also seems strange that I was told that the inverter can't work with the battery when the battery voltage is below 50V. That must surely be a design fault.

It's a safety thing I think. So ordinarily it's a good thing. Just not ideal for these occasions.

I'll put it down to experience. Thanks for taking an interest!