Warning lights

Hi, i have posted before regarding my 2014 3.0 TDI and warning lights. The TPMS, flat tyre and traction control lights came on along with a stability warning message. After stopping, turning off ignition and restarting, they went off. This has happened about 3 times in last 10 months. I got codes read and it come up with an ABS pressure fault. I arranged with the seller (through warranty) to have the pump repaired/replaced and took it the 100 miles to them and left it for a week. there were also signs of a weak battery, slow cranking, stop/start slow to react along with the steering going stiff. After a couple of days, they called to say they couldn't start the car to read codes and battery was too far gone to recharge and so replaced it (at a cost to me of £240.00, which i was fine with as it was a Bosch and i didn't want to really remove seat!). When they came to read codes, there were none stored but the cranking was fine, as was the steering. They drove it round for a few miles over the next few days with my permission but the ABS fault never occurred so was put down to low voltage and i got the car back. After 2 weeks and about 30 miles, got the same warning lights and message again! As soon as the ignition is turned off and on again, they disappear for the next few days/weeks/months! There doesn't seem to be any effect on driving. Has anyone got any suggestions?

Gary.