Electrical gremlins in my 118d coupe

[jhpgram]

So I have recently purchased a 118d Coupe to run as a daily driver alongside my Z4 Coupe. I bought the car for a good price and was aware of a few issues.

The most prominent issue I was aware of was the fact it didn't have the correct AGM battery. So a few of the issues I faced from this (or so I think to be from it) - every time I start the car after leaving it the clock, trip odometer, MPG, date etc all reset, the bluetooth, aux don't work, start-stop and hill assist...all completely inoperable.

So, I replace the incorrect 75Ah battery with the correct OE spec 95Ah Varta battery and got it coded to the car. Was told the car would need to "sleep" as well to learn it has had a new battery, but nothing.

After some research, I was led to believe the Intelligent Battery Sensor could be faulty and shutting things down, so I disconnected that...still everything resetting etc.

Will keep looking for answers...has anyone else faced these issues? My solution might end up being some petrol and matches

(Edit)

Assuming these issues were initially caused by the incorrect Ah battery making the car read as low voltage and shutting down power drawing devices such as bluetooth etc...

TIA

[Lester]

You will need to have the battery coded into the computer to register it as a new battery.

[NorthernDancer]

Many electrical issues are caused by loose, dirty and/or corroded battery cables ESPECIALLY a ground cable very low on the left side of the engine. I'd recommend taking it to a shop that knows BMW's.