Originally Posted by Pfflyer
As stated in the Sprinter forum, I use a Battery tender plugged into an always hot 12v outlet connected to the chassis battery. I am not sure if the latest version Sprinters have this but it should say in your owners manual or you could test the chassis 12v outlets while the ignition is off.
This is actually what I do when my rig is sitting for a while. I was going to install a Trik-L-Start to keep the chassis battery charged, but I had an extra battery tender sitting around, so I just plug the battery tender into the outlet under the dinette, and I put a male plug on the output, and plug it into one of the dashboard receptacles, that are hot all the time from the chassis battery.
During the Winter, instead of having the complete 120 volt system energized when plugged into shore power, I ran a second battery tender to the house batteries. I didn't want to pull all the batteries out, in case I needed to move or use the rig during the Winter.
Then, I put a digital timer on both of the battery tenders, so they only cycle on twice a week. This is more than enough to keep the batteries topped off, without needing them to be plugged in 24/7.