I have a 2016 GLC 300. Wife has new 2019 RDX. ECO Start Stop new to her.. Reminded me that I could not remember the last time mine engaged. The ECI button shows Green. Please no posts on the reasons it not supposed to come on. Saw several post indicating its probably a battery, voltage regulator or sensor issue with or falsely indicating low voltage. No indications of a low battery. Several long drives so battery should be fully charged. No urgency, but will make service appointment.