Adding a second battery- should you use a VSR? I have a 2019 144 passenger rear wheel drive, diesel.

Hydrosrv

New member
Please excuse if this has posted before but I could really use the help.
I purchased a KeyLine Chargers 12V 140 Amp Dual Battery Isolator Voltage Sensitive Relay (VSR) Pro Dual Battery Kit.
The reason for my inquiry is I was told that I could not use the VSR because my alternator is a "smart alternator". I am a little confused and don't want to screw up my van.
If there is a better option or some one has a better idea, would you be kind enough to let me know? Pictures or schematic would greatly help.
Thank you for considering.
Cheers
Dave
 

Hydrosrv

New member
Hello RV Barry
Very good of you to reply.
Just the stock MB battery, I would guess just a AGM. The battery I would like to install is a 100 amp/hr AGM as well.
I am looking at ways to charge from my existing alternator. I have already purchased a VSR kit.
Thanks
Dave
 

Langhammx

New member
Hello RV Barry
Very good of you to reply.
Just the stock MB battery, I would guess just a AGM. The battery I would like to install is a 100 amp/hr AGM as well.
I am looking at ways to charge from my existing alternator. I have already purchased a VSR kit.
Thanks
Dave
2020 144 high roof…
I’m in the exact same situation. I am adding an AGM battery for mostly the stereo system and some LED interior lights that I added, along with an inverter that will rarely be in use. I have read too many threads and various opinions…so I’m looking forward some clarity myself on this job.
I do know that the alternator is “smart” and will detect it. I decided to just use a Blue sea battery link.
A9656BE1-5307-4BFD-AAD4-D16A9D96D426.jpeg

But I have not decided where I will attach to the vans electrical system. I’ve read to NOT tie it directly to the battery post, although there is a perfect spot for it.
C922E650-8746-4B8D-A85E-084C5D9DA7D0.jpeg

I have an appointment at Rocco’s on Friday to activate my rear fader for the stereo and hook up the pins to the plug off the radio. While I was there, I asked him the best spot to hook it up and he said to just bolt it down to the existing #5 spot with the large RED cable-
F004A0FA-8D23-4C3B-885B-0A4E6BAA1C17.jpeg

I’ve also seen others who have added a lug to the buss that is bolted down to the right (rear) side of the battery…
39826EB5-AB66-45A9-AA40-CDCF7B4614CF.jpeg

While it may not even matter, since the alternator will charge the auxiliary battery anyway, but mounting it to the threaded post on the battery itself would be the easiest/ cleanest and plenty of room for a 250a fuse link that I can Velcro on top of the Van battery.

Any help/ suggestions would be greatly appreciated. I gotta make a decision today and get the van back together

Thanks, Shaun
 

RVBarry

2023 AWD 170 DIY CamperVan
Hello RV Barry
Very good of you to reply.
Just the stock MB battery, I would guess just a AGM. The battery I would like to install is a 100 amp/hr AGM as well.
I am looking at ways to charge from my existing alternator. I have already purchased a VSR kit.
Thanks
Dave
If both batteries are AGM, a relay will work fine even with the 'smart' alternator profile.
 

Hydrosrv

New member
2020 144 high roof…
I’m in the exact same situation. I am adding an AGM battery for mostly the stereo system and some LED interior lights that I added, along with an inverter that will rarely be in use. I have read too many threads and various opinions…so I’m looking forward some clarity myself on this job.
I do know that the alternator is “smart” and will detect it. I decided to just use a Blue sea battery link.
View attachment 185690

But I have not decided where I will attach to the vans electrical system. I’ve read to NOT tie it directly to the battery post, although there is a perfect spot for it.
View attachment 185691

I have an appointment at Rocco’s on Friday to activate my rear fader for the stereo and hook up the pins to the plug off the radio. While I was there, I asked him the best spot to hook it up and he said to just bolt it down to the existing #5 spot with the large RED cable-
View attachment 185692

I’ve also seen others who have added a lug to the buss that is bolted down to the right (rear) side of the battery…
View attachment 185694

While it may not even matter, since the alternator will charge the auxiliary battery anyway, but mounting it to the threaded post on the battery itself would be the easiest/ cleanest and plenty of room for a 250a fuse link that I can Velcro on top of the Van battery.

Any help/ suggestions would be greatly appreciated. I gotta make a decision today and get the van back together

Thanks, Shaun
Very good of you to write and I thank you. Would you be kind enough to let me know what your final decision is?
 

borabora

Well-known member
You aren't going to harm your chassis battery or your van by using a reasonably sized house battery separated by an isolation relay. The problem with a VSR and a smart alternator is that the alternator will lower the output voltage because it thinks or knows that the chassis battery is fully charged. That lower voltage may not be enough to fully charge your house battery. AGM batteries don't like to be not kept fully charged. Chronic under-charging AGMs will reduce their life expectancy. So keep an eye on your house battery's charge status either by using a battery monitor or by following the correct measurement procedure (google it).
I believe your van's chassis battery has a shunt that informs the van of its state of charge. There are arguments to be made for connecting the VSR inside or outside of the shunt. Best to refer to the upfitter's manual for the best strategy.
 

Mendeleev34

Active member
I have a blue sea ACR in my van for alternator charging of my house battery and it is not working (2019). As borabora states, the voltage is likely not high enough to charge the house battery, since the electronic control ("smart") is trying to maximize fuel economy. I'm trying to fully verify the situation but I have very little time for troubleshooting with work and kids. I'll post more when I get to the bottom of it, but I'm fairly convinced I will need a Sterling B2B unit instead.
 

Langhammx

New member
Very good of you to write and I thank you. Would you be kind enough to let me know what your final decision is?
I ended up hooking up to the lug with the largest cable, under drivers seat. I bought the blue seas 250a fuse and grounded my battery cable (from the auxiliary battery) to the ground stud under the drivers seat. Everything is working great, no issues and the battery is definitely charging without an issue !
DBECAE3E-43AD-4A73-A6B4-19FF736A1CFA.jpegC2B3D9C9-3971-4D4E-A129-4EEF45009DFA.jpeg

I forgot to take a pic with fuse installed, but I shortened the cable and it looks very clean/ tidy now !
 

Kajtek1

2015 3500 X long limo RV
I hooked up dual house batteries to smart charging system and it was smart enough to handle it just fine.
My van had fuse board attached to the main battery, so I just add fuse there and then most of Sprinters have converter board, so cheap 100 amp relay makes for foolproof system.
Still I drove with ScanGage showing the van voltage to make sure I had no surprises.
AGM and flooded batteries are the same chemistry-wise.
Only difference is that AGM are a bit stronger and can be operated upside down.
I just bought $80 battery at Costco for my house bank.
 

Hydrosrv

New member
I ended up hooking up to the lug with the largest cable, under drivers seat. I bought the blue seas 250a fuse and grounded my battery cable (from the auxiliary battery) to the ground stud under the drivers seat. Everything is working great, no issues and the battery is definitely charging without an issue !
View attachment 186151View attachment 186152

I forgot to take a pic with fuse installed, but I shortened the cable and it looks very clean/ tidy now !
Thank you so much for the considerate reply. I intend to copy what you have done. Very good of you to help me out.
Cheers
Dave Walker, Jamestown, Rhode aIsland
 

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