R26 Total loss of electrics

On friday morning when i went to leave for work, the car wouldnt start. I was getting numerous messages come on the the dash, "steering fault" "brake fault" plus loads of randoms symbols and letters. The car would also constantly try and double lock itself. Long story short, i ended up having to get breakdown people out and he quickly determined the battery was nakered. A quick jump from his machine and it was running. He ran a test on it and the alternator was at 100% and battery at 0% life. He suspected it was the origional battery.

So i got to work, and ended up fitting a new battery in the carpark. All seemed well, reset the esr, elec windows, clock etc.

Now this morning on the way to work, as i was approaching a junction i indicated left and began breaking when all of a sudden i lost all my electrics. After about 2 seconds they came back to life. When i got to work i just had to reset everything as above.

Now on my way home tonight, i had to pull over to fire up my sat nav as the police had closed the road due to an accident. As i began to pull over onto the curb, total loss again. Even my steering went, maybe it was just like having no power steering but i could barely turn the wheel. The entire dash went out, head unit off, dash cam which was plugged into cig lighter went, but for some reason the needles on the speedo etc stayed up where they were before the power went out. After about 10-15 seconds the engine then stuttered and died.

I tried taking the key card out and starting again, but the engine did nothing, windows would'nt work etc. The only thing that did work was the hazards which had come on by themselves....

After 10 mins of me swearing at the bloody thing it just came back to life as if nothing was wrong. Again, had to reset esr, windows etc. Got the car the 20miles home without any more issues.

Any idea what the hell would cause the power to go like this?

Thanks