Electrical fault, sports differential fault and high idle speed 50TDI

[ijm1965]

On my drive to work Friday after about 7 miles the yellow battery symbol and a message electrical fault contact workshop message came up quickly followed by sports differential fault. When I finished my journey I noticed the idle speed was very high - maybe 900 rpm the same as cold start running.

On my journey home that evening no error messages but noticed the stop start didn't work. However went out an hour later and all back to normal.

I have had the car 6 years so I am used to the fact the error messages are cryptic puzzle and don't really help much. When I had these messages before it was the lead acid battery on its way out and after a while also had low cranking speed when cold. So I am assuming this probably means a low voltage causing the errors and the high idle speed was the car trying to give the battery an extra bit of juice.

The battery is only about 18months old can they fail that soon (its an Audi supplied spare)?

What is the cheapest way to get the codes out of the car for some proper diagnosis?

[robgr]

Assuming it's not the battery monitor then there is a separate lithium battery that provides the stop start function which may be faulty

This part is not included in any extended warranty and would cost around £800 to replace

The battery only has a manufacturer warranty for 6 months or 6500 miles from new; after that, it would be classed as wear and tear for the battery