I've twice now found that after listening to the radio for ten minutes while parked the screen gives me a message telling me to turn the radio off as it's flattening the battery!

 

I'd have expected the battery to be able to power the radio for many hours, if not a few days. 

 

Does this suggest a faulty battery or is it a known syndrome with Octavias?

 

It normally happens after 30 minutes and not 10 IIRC.

You can turn it back on again after that but it's to prevent you forgetting about it being on and the battery going flat.

Murmansk...............I'd suggest that either your battery is starting to fail or you're not doing enough driving to charge the battery up and the battery saver circuit is kicking in to save what little power is left to enable you to start the car.  I had the same problem with my previous car, Mk 3 Focus.  That would turn off after 10-15 mins.  Had it checked under warranty and in the end Ford authorised a new radio unit costing £700 to be fitted.  The fault still persisted.  It was only after talking to the mechanic at Arnold Clark that he suggested as I was only using the car for short trips at the time that the battery wasn't being fully charged.  I bought myself a smart charger and connected it up to the car for a couple of days and it cured the problem.  Now that I have an Octavia and only do short trips occasionally I still connect the smart charger now and again and have never had a problem.  This may not be your problem but worth a thought.

Hmm, thanks for that, I'll maybe take it to a place I know and trust for them to check the battery and see what they say

I take it as a useful warning. Maybe shorter journeys trigger it as well. A Kia Picanto 3, less than a year old flags this up as well.