'03 eclass 220cdi power issues

[Taylor220cdi]

Hi, first post so please bear with me

My 2003 e class seems to need to be running for about five minutes before all the electricals will work such as interior lights, demist function etc... There are no starting problems, almost as if the battery needs a little time to charge up and get going. Any suggestions ? Current thoughts are aux. Battery needs replacing but don't want to lead myself down wrong path...

 

[Taylor220cdi]

Fixed thanks to replacing both - yes both - batteries. Mb dealer cheaper than halfords too