mobymidge

FxFormat

I had the same issue, turns out to be a bad battery control module, it was starting to burn up too, might want to open your trunk and pull the liner back and check out the BCM.

S-Prihadi

This seems to me , is not a battery issue, this is intermittent or bad contact on some power source or its relay/s or fuse/s, to those items/devices you explained as dead until engine run for a short period.
Clock reset to 12:00 usually means power was totally lost at some point to the clock.

The repair or replacement of parts you mentioned could have failed to cover/replace a 100% of the water damaged components.

For example, let say the workshop replaced a corroded fuse block/housing but did not change the wiring harness to and from the fuse block.
TO is the upstream of that fuse block.... its main power, FROM are devices connected or served by that fuse block. All these has connectors.
Connectors can corrode at the metallic terminals itself or it may corrode at the wire to terminal crimpings.
Even the fuse legs can corrode.

This kind of troubleshooting takes time and patience and a complete wiring schematic and fuse assignment chart to speed up the job.

YOU WROTE :
AA. Every time I start my car I am presented with the convenience offline message as well as the clock being reset to 1200. BB. After a short period of driving the message will disappear and all is good until I park up again. CC.If I return back to the car again it seems that all the electrics are offline (central locking doesn’t work, no interior lights) until I start the car with the key again. Once the car is started again the clock is back to 1200 and the convenience offline message is back.

If going by AA only , it seems the 12 volt supply to those devices are "lost" when you turned off the engine and removed the key, where by they are supposedly from a constant power.
If going by BB only, and since you mentioned AFTER A SHORT PERIOD OF DRIVING yada yada ITS ALL GOOD .... you are describing as though as a low voltage situation which after a short drive and with the alternator feeding power, the low voltage situation becomes normal or minimum normal operating voltage and those devices work again.

If we combined AA , BB and CC, what may happen is when alternator is not running at approx 14.1 volt, those devices you mentioned was having voltage below its minimum requirement and it is in OFF state, like zero power.
Remember, a clock would be running from a constant power supply and so are power lock and interior light.

If I were you, I will find the fuse/s which feed power to those 3 devices and measure for low voltage when engine is off and see how much voltage rise when engine been running a while and is still running.
Corossion creates resistance.

If zero voltage to the fuse/s for those 3 devices when engine is OFF, then somewhere up stream there is probably a relay which could be bad or also effected by low voltage on its coil.

Good luck troubleshooting

bobterry99

Prior to starting the car I would measure the voltage on the rear battery. If it is significantly greater than 10.8 volts, then I presume the battery control module is faulty.

mobymidge

Thanks everyone. I followed bobterry99's advice and checked the battery voltage again and found only 2 volts on the consumer battery. I have tried charging the battery but my CTEK kept going into error mode. I have now returned the battery and had it confirmed as defective. This is a surprise considering the battery is less than 10 months old. The one thing I have learnt is that testing the batteries while still in the car and connected can give false results as the battery shop pointed out that when I had the consumer battery tested it may have actually been reading the main battery in the engine bay.

Anyway, the battery has been replaced under warranty and all is good.

Frederick NL

Frederick NL