ECU and battery Problems

[snapdragon]

I too have had this recently.
My battery is only 6 months old VARTA and coded correctly.
Software is 5570.

I parked on the road and left the sidelights on for maybe 4 hours and when I returned the keyless entry had stopped working, a sign of a low battery.
When inside, I checked the meter and it said 10%.
The car started but judging by the dashlights flashing off it was a struggle.
By the time i got home 7 minutes later, it was on 60%.

The next day, it got up to 80% on the way to the shops and I left the blowers on for 45 mins and when we returned the battery was flat, so I called the green flag and they started it and said it was charging low at 12.6V.

When I got home ( a much longer journey than the night before) it said 30%. So I charged it from the mains. I also disconnected the battery and reconnected and now it charged at 13.40V.

It has been for 3 days since.

I think when the battery gets low, it scrambles or crashes some module, maybe the power manager or something and so disconnecting the battery resets everything. Then clear all the codes with VCDS.