Just finished hardwiring battery tenders for both the front starter and the rear AUX batteries. For the record as a disclaimer, I'm not claiming to be an expert electrician so read as entertainment if you're not the type to DYI. I've researched for days and even called some Mercedes techs, I didn't get a definite answer of where to install the tenders. After ripping out the panels in the trunk to access the rear batt and to see if it's easily able to run to the front so that both tenders can be plugged in the same area rather than f/r of the car, I gave up. It's much too difficult to run the wire thru the rear seats and along the edge of the car. I ended up using a volt meter to look for terminals around where the starter batt is. Looks like there were quite a few that links to the AUX batt. I picked the biggest one that looked like it wasn't used for anything else up front and mounted to that. Manuals and diagrams weren't helpful to see what all the terminals were for. I felt it was safe enough per testing with the meter. It's been a few days and everything looks like it works as should. With these new heavily equipped electronic cars, tenders are a must. My other cars with tenders on them have all lasting over 10 yrs and still going. Once a non deep cycle battery dies out, it's never to be trusted again . Hope this can be some type of contribution for being helped earlier.

The terminal with the finger pointed is the connection.




Being charged.




Capped and ready to go.

 

That's where I put my tender during that last winters when keeping my CL in the garage, no problems...the starting battery usually doesn't need a tender.

 

Thanks for the reassurance Tx.