Hey guys so just fitted new battery and the HDC fault is still showing, any other ideas

A bit more info would be handy, FL2 Model/Year, any OBD Codes, any other Symptom.

Have you done a hard reset and/or cleared any OBD Codes with the battery change.

The FL2 fault system can retain code faults and symptoms for some time after fault has occured.

Search on FL2 site gives this

https://www.freel2.com/forum/topic39588.html?highlight=hdc

https://www.freel2.com/forum/search.php?se...rch_time=0 FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 84k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)