Acidic smell in cabin when starting from cold

[The LB]

Hi, looking for some help please. Over the last week I've noticed an acidic smell in the cab when the engine is started from cold first thing in the morning. Smell goes away after 10 minutes or so when driving. I had the rear EGR pipe replaced last year and the new one looks ok with no leaks. Any ideas? Thanks, Rich.

 

[JumpShip]

Do you have a leisure battery fitted ?

 

[The LB]

We do, though it's a lithium one fitted in the rear of the vehicle with the smell coming from the cab area. No smell around the battery.