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  • 1 year later...

@Gr8FrozenNorth : did you ever complete this operation of adding the auxiliary battery and increasing the alternator capacity?


I just purchased a 2021 2500HD LT and they "forgot" to install the package or couldn't due to missing parts.  Anyway I have the parts ordered and a new 220 volt alternator on the way and will be doing this mod in a few weeks when everything arrives.


My truck arrived with the 170 Amp Alternator but has a 250 amp fuse for the alternator on the main battery.  For a 170 amp alternator this would normally be a 175 amp fuse.  For some reason my fuse block is from a 1500 Diesel with a 220 Alternator - for me, that is a good thing :)


I purchased the " J Block Auxiliary Battery"  84663447 - this part comes with a 30 amp fuse, a 100 amp fuse and a 175 amp fuse.  The 100 amp fuse is connected to an isolator relay all as one assembly.  The cover is Junction Block Cover 84471670


I am re-using the cable from the main battery positive to the terminal on the X50D (175 amp) it runs from the main battery over to the X50A Fuse Block (as per normal) and then a short pigtail will run from that connection to the 100 AMP fuse on the auxiliary battery J Block (X50E).  this is the fuse attached to the isolator.


The isolator is supposed to be powered from a secondary relay that wires into a connector X136.  I have to find all that on the truck first but I am away on business so it will take a bit.  right now I am still in research mode but it looks like that is pretty much it other than connecting the trailer 30 supply power wire up.


From reading the battery relay will energize if you switch to tow/haul mode and it will charge the aux battery. 


maybe someone with the factory install would have more intel.  I will post pictures once things get underway.  

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I'm wondering if anyone has had their dealer do an install much like the factory install? I just put a deposit on an in transit SLE with the Snow Plow Prep so I will have the 220A alternator. I would just need the battery, the new junction/fuse box and the additional leads. I know as a factory install its like a $135 install but looking at the parts list it looks significantly more as an after the fact installation. I just wasn't sure if there was a retrofit kit for the dealer to order of if you need to identify and order the individual parts needed.

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My new 3500HD gas truck arriving next week will have the factory dual battery installation.  If you would like me to post photos of anything let me know.  I'm going to be immediately installing 6awg wire to a slide in camper connector (for a 30 amp DC-DC converter/charger in the camper), so figuring out the battery, isolator, and fuse block arrangement on the truck will be one of the first things I get into.

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