Hi Folks,
I finally had to replace the AGM original batteries on my 2016 MB. Found these Wattcycle brand mini size 100AH lithium batteries for a good price.
Was able to fit 3 in the battery compartment without any cutting or modifications. I added a Victron smart shunt and still need to order and install an Victron Orion 50amp DC to DC converter to go in the alternator charge line to the batteries.
I did install some small 12 volt bee keeping heater mats underneath each battery to keep them above freezing. They have low temp protection in the BMS, but I can heat them as needed by inserting a fuse into the fuse holder. Will probably put a toggle switch in instead. I did upgrade the converter to a 75amp PowerMax PM4, was able to fit it in the old parallax lower housing.