Rear Parking Sensor Issue + Fast Blinking Indicators

[reganpickles]

2019 T6 T30 with rear parking sensors only no camera
I had a dual battery installed under the seat by a local 4wd company who do a lot of 12v installs in March this year and had no issues until end of July when it stopped charging.
A few days after it had stopped charging a start/stop error came up on the dash, the glow light (as if a light is out) and my blinkers started flashing fast on the dash but normal speed outside.
At the same time as this my rear parking sensors stopped working. I just get a long beep when I put it in reverse and a message on the screen saying 'Parking Pilot is Unavailable'
I took the van to VW who I bought it off and they traced it back to getting no power under the passenger seat and we're blaming the dual battery installer.
Today the van went back to the dual battery installer and they corrected the issue of the battery not charging and my start/stop error has gone away.
Have attached screen shots of my carista of what I'm getting as well as what VW has said.
I've also tonight put the van in reverse with the engine off and I can hear each individual parking sensor making it's 'clicking' noise
Appreciate any help

 

[Pete C]

Has the battery installer explained what they fixed ?

Pete

 

[reganpickles]

Has the battery installer explained what they fixed ?

Pete

Under the passenger seat when I bought the van it had wires but no battery (assume owner took out before trading van in to dealer). The battery installer just used the power from one of those wires to power the charger. Today he ran a new wire from the crank battery to the charger and it sorted the charging issues

 

[reganpickles]

Think I may have found it. Looks like whoever had the van before me has tried to screw something down (battery tray maybe) and has gone through the harness. All the fuses under the battery in the engine bay are fine