Guide to Disabling Auto Start Stop + Removing the Auxiliary Battery on a 2025 RAM 1500 SO/HO

[turbom5]

Posting this to help others who may want to remove their auxiliary battery to diagnose or prevent issues like voltage drops, no-start events after the truck sits, or similar problems.

What This Modification Achieves:

1. Removes the auxiliary battery, which many suspect is a source of battery issues (voltage drops, no-starts, etc.). This battery primarily exists for the Auto Start-Stop function.
2. Allows you to upgrade your main battery to a longer, higher-capacity H8 size (it bolts right in).
3. Disables the Auto Start-Stop function.
4. In my testing, this caused no error codes. I verified using an AutoAuth subscription and an XTOOL scanner capable of reading and clearing all modules.

Vehicle Tested On: 2025 RAM 1500 SO

Note: Someone else performed this on a 2025 RAM 1500 RHO and reported the same success in removing the aux battery, but claimed it did not disable Auto Start-Stop. On my truck, it has not engaged Auto Start-Stop once under various conditions since the removal over a week ago—even with HVAC off, at operating temperature, and during drives over 30 minutes.

Instructions:

1. Disconnect and remove both batteries. Use a 10mm socket (nut on left side for main, right side for aux).
2. Disconnect the N3 lead on the left side of the under-hood fuse box. This is connected to the positive cable running to the auxiliary battery.
3. Pull the F52 10A (PCR CTRL FEED) fuse in the under-hood fuse box. This disables the system's monitoring of the auxiliary battery.
4. Tape off or disconnect the negative cable that went to the auxiliary battery.
5. Remove the small plastic spacer at the bottom of the battery tray (between the two battery compartments). This piece limits you to an H7 battery. Removing it and the Aux battery creates space for a longer H8 battery, which will secure using the OEM H7 battery holder. H8 batteries have more cold cranking amps and capacity as the H7 and are phyiscally longer.
6. Re-install the main battery.

Results & Benefits:

• Auto Start-Stop is disabled.
• Eliminates a known failure point—the small, problematic aux batteries that can fail and even drain the main battery when the truck sits.
• If your aux battery has failed, you save the cost of replacing it (~$150 USD /~$200 CAD).
• The modification is completely reversible.
• Bonus: You now have a spare 12V battery (the removed aux) for other projects.

Personal Experience: After over a week of testing in temperatures as low as -15°C (5°F), the truck starts reliably even after sitting for days. I'm now finding resting voltage between 12.0V - 12.5V, whereas with both batteries installed, it was commonly 11.0V - 11.7V or lower. The aux batteries have been known to draw down on the main battery ending up draining both batteries.

Technical Note on Fuse F52 (PCR CTRL FEED) & the ESS System (Auto Start Stop):

For those interested in the why, Fuse F52 is the control feed for the Power Control Relay (PCR). This relay is key to the Auto Start-Stop (ESS) system in dual-battery trucks.

• The PCR is a normally closed relay. This means when it's not energized, the main and auxiliary batteries are connected in parallel (which is how a failed aux battery can drain the main).
• The system only energizes the PCR to open (separating the batteries) during two events: 1) for a moment at startup to test the aux battery, and 2) during an ESS event to isolate the electrical loads to the aux battery.
• By removing F52, you remove power from the PCR control circuit. This leaves the relay permanently closed. However, with the aux battery physically removed and its leads disconnected, the system cannot manage the ESS function, leading to its disabling the ESS Auto Start Stop system.

*(This PCR concept is shared with other Stellantis vehicles like the Jeep JL Wrangler. Note: eTorque models with a 48V battery do not have this aux battery/PCR setup.)
*This is the same method used on numerous stellanits dual battery vehicles from 2018-2024 with the same results.

Common Issue Across Stellantis Vehicles​

The auxiliary (AUX) battery and Power Control Relay (PCR) system used in the 2025 Ram 1500 is not unique. It's a shared design across many Stellantis vehicles with Auto Start-Stop (ESS), including Jeep Wrangler JL, Jeep Gladiator, Dodge Durango, and Chrysler Pacifica. Owners of these models have reported identical problems and use virtually the same fix.

The Core Problem:
The small, low-capacity AUX battery is a known weak point. When it fails, it can drain the main battery because the system often keeps them connected in parallel when the vehicle is off. This is a frequent cause of the "dead battery after sitting" issues reported across forums.

The Common Solution:
The fix involves two steps:

1. Physically disconnecting or removing the AUX battery.
2. Disabling the PCR control circuit to prevent the vehicle from looking for the missing battery and throwing errors.

This is typically done by pulling a specific fuse (e.g., F42 in Jeeps, F52 in the 2025 Ram) which cuts power to the PCR relay. An alternative method is to unplug the PCR relay itself, which is more physically challenging.

Examples from Other Platforms​

Vehicle	Common Fix	Key Forum Discussions
Jeep Wrangler JL / Gladiator	Pull Fuse F42 ("PCR CTRL FEED") and disconnect the AUX battery negative cable.	The "jumperless" bypass method is well-documented. Users confirm this disables ESS and prevents a failed AUX battery from draining the main.
Chrysler Pacifica	Unplug the PCR relay signal wire (functionally identical to pulling a fuse) and disconnect the AUX battery.	Detailed guides explain that bypassing the PCR allows the system to run on the main battery without error codes, while also noting the design flaw that lets a bad AUX battery kill the main.
Dodge Durango	Discussions center on locating and disabling the PCR relay to bypass the AUX battery.	Forum threads seek and share methods for the PCR bypass, indicating the same underlying system and issues.

 

[NorskieRider]

Feedback on whether this also applies to the 2026 would be appreciated!

 

[Diesel]

This is an amazing and detailed procedure to eliminate start/stop, which is in fact controlled by the AUX battery, but I am not convinced the AUX battery is the culprit for draining the main/primary battery--that is a problem of the key fob being too close to these vehicles. Hang the key far enough from the vehicle that when you get near it, passive systems don't detect your presence and become active every time you get near it.

I tested this extensively after having both batteries die after many passive sensors became active--headlights/taillights activated, RAM logo displayed on garage floor, retractable steps deployed/redepoyed...ect. Yeah, that will drain the batteries in no time, which it did. I wasn't having any of this and replaced both with Antigravity Lithium Batteries and have never looked back.

P.S. The AUX battery is a helpful backup battery to start your truck if the main dies, so I'm keeping it

As far as the Start/Stop tech, I just simply get in my truck and push the disable button...

 

[Carlos.33193]

I was thinking of removing aux battery, replacing main battery with H8, and running some 0 gauge wire from main battery to aux battery terminals in order to simulate the aux battery still being installed so that there's no issues with anything in the truck not working as it should or throwing codes etc.

Has anyone done this or have any feedback on doing this?

 

[firemedic10584]

I really like this and appreciate you taking the time to detail all this out. My 2026 already had the dead battery issue 1 week after buying it. I haven't had any issues since, granted it's only been a few weeks now. But I'm definitely considering following this and going this route.

 

[Carlos.33193]

I was thinking of removing aux battery, replacing main battery with H8, and running some 0 gauge wire from main battery to aux battery terminals in order to simulate the aux battery still being installed so that there's no issues with anything in the truck not working as it should or throwing codes etc.

Has anyone done this or have any feedback on doing this?

I was installing an inverter today and decided to do this.
I removed the H7 and Aux battery, and replaced it for a single H8 battery.

I had to remove a small plastic clip-in bracket that's at the bottom of the battery tray so the H8 can sit in there. The battery insulator jacket doesn't quite fit, it's too small as the new H8 battery is about 2 inches longer.

I drilled a hole in the terminal connector to attach the negative from the AUX battery, and I ran some new 4-gauge wire from the positive to the positive of the aux battery and clamped them together with bolt and nut. I don't recommend doing it this way, I will eventually go back and add a fuse in-line there. I put a plastic sleeve to cap off the connections and then taped it.

Truck didn't show any issues or anything, and Start Stop still works and everything works as before. Incase the AUX battery is used for more than just ESS i decided to do it this way.

 

[firemedic10584]

I was installing an inverter today and decided to do this.
I removed the H7 and Aux battery, and replaced it for a single H8 battery.

I had to remove a small plastic clip-in bracket that's at the bottom of the battery tray so the H8 can sit in there. The battery insulator jacket doesn't quite fit, it's too small as the new H8 battery is about 2 inches longer.

I drilled a hole in the terminal connector to attach the negative from the AUX battery, and I ran some new 4-gauge wire from the positive to the positive of the aux battery and clamped them together with bolt and nut. I don't recommend doing it this way, I will eventually go back and add a fuse in-line there. I put a plastic sleeve to cap off the connections and then taped it.

Truck didn't show any issues or anything, and Start Stop still works and everything works as before. Incase the AUX battery is used for more than just ESS i decided to do it this way.

So you essentially just connected the positive and negative leads originally on the aux battery to the main battery now instead?

 

[Carlos.33193]

So you essentially just connected the positive and negative leads originally on the aux battery to the main battery now instead?

Yes. No voltage or internal resistance differences between 2 batteries. Not sure why Mopar didn't just do it this way from factory and run the bigger h8 in the first place.

 

[turbom5]

Yes. No voltage or internal resistance differences between 2 batteries. Not sure why Mopar didn't just do it this way from factory and run the bigger h8 in the first place.

Do you really think they engineers didnt think of that ? Sure would save alot of money not needed a PCR system designed and installed in every vehicle or a second battery and extra fuses, etc...

The purpose of having the second battery is to prevent voltage drops and load on the main during start stop when the engine is off. The electronics all run off of that small battery solely during the stop event. The main battery is used for starting the engine in all cases.

It's a good design to stabilize voltage. These vehicles are sensitive to voltage drops as any modern high tech vehicle is.

It was essentially added due to start stop. To stabilize voltage while engine is off.

By removing it you should be disabling auto start stop as well especially since your idea was to not affect the electronics of the truck and not get any codes.

This method is not a replacement for what I described which is the method used across various stellantis product lines since 2018 for removing the aux battery.

You should be pulling fuse F52 if doing this to prevent the PCR from cycling and from auto start stop from occuring so you're main battery isn't carrying that load with the engine off.

If you did a bit more research into the PCR and purpose or the aux battery you would understand why it's there and how to properly remove it without creating other issues down the road.

Not a good idea simply connecting them together and doing nothing else.
The PCR still cycles thinking it has an aux battery.
The main battery suffers during auto start stop while the engine is off carrying the load of all electronics and then carrying the load of starting the engine over and over again. The exact job of the aux battery was to carry those loads and stabilize voltage.

Sure you may not notice any issues during a limited number of start stop events on your new higher capacity battery but If you thoroughally tested it in numerous sequential prolonged start stop events in various conditions you'd like find there is voltage drops and issues. The engineers designed it to work reliability in wide array of conditions under numerous start stop events and over time as the batteries weaken. This is a bad idea without pulling fuse F52.

 

[turbom5]

1. The wiring solution is overcomplicated and creates risk. Running 4-gauge wire to bridge the terminals introduces an nnecessary failure point—a live, un-fused positive cable that could short to ground. The clean, correct method is to simply disconnect the unused auxiliary positive lead at the 12mm nut on the under-hood fuse box (the N3 connector). This eliminates complexity and risk.

2. You are defeating the system's purpose. By removing the auxiliary battery but leaving the PCR/ESS system active, you force the main battery to carry the entire electrical load during engine-off stops. This sets up for voltage drops when cranking, especially during prolonged stop cycles or repeated start-stop events in extreme heat or cold.

3. The proven method is complete and simple. The established, 8-year proven fix is three steps: 1) Disconnect the auxiliary battery, and 2) Pull the F52 fuse to disable the PCR/ESS control. 3) remove unused positive lead via 12mm nut on N3 at fusebox. This safely and logically removes the aux battery and is reversible.

In short: Adding wiring creates new problems. Skipping the fuse pull ignores the core electrical logic and stresses the main battery. The standard method addresses both and is proven to work without issue over time.

 

[Carlos.33193]

You are correct, my method is not good. I went back and tried to do it with what you posted. But my truck is missing F52 fuse, I unplugged battery aux + by disconnecting N3 and taped off the aux negative.

I figured because I don't have F52 it should just work.

Are the 2026 different? Mine is a limited. Again, no F52 fuse, I just unplugged aux battery and the N3. Is this ok?

Went for a drive. No errors or messages and then auto start stop kicked in, truck died and won't start again even though voltage reads 12.4, have check engine light, transmission shifter lights all flashing. I think the missing F52 fuse has something to do with it? P.s was able to unplug battery and start again, but have some obd codes.

I think this method is not working as foolproof as it should on my truck due to F52 missing.

 

[Jimmy07]

You are correct, my method is not good. I went back and tried to do it with what you posted. But my truck is missing F52 fuse, I unplugged battery aux + by disconnecting N3 and taped off the aux negative.

I figured because I don't have F52 it should just work.

Are the 2026 different? Mine is a limited. Again, no F52 fuse, I just unplugged aux battery and the N3. Is this ok?

Went for a drive. No errors or messages and then auto start stop kicked in, truck died and won't start again even though voltage reads 12.4, have check engine light, transmission shifter lights all flashing. I think the missing F52 fuse has something to do with it? P.s was able to unplug battery and start again, but have some obd codes.

I think this method is not working as foolproof as it should on my truck due to F52 missing.

Is your truck a limited, tungsten, or RHO? There seems to be a big difference in the dual battery switch schematics on trucks that have L2+ decision making module equipped trucks, vs regular lane assist equipped trucks.

 

[Carlos.33193]

Is your truck a limited, tungsten, or RHO? There seems to be a big difference in the dual battery switch schematics on trucks that have L2+ decision making module equipped trucks, vs regular lane assist equipped trucks.

Yes, it is 2026 limited.

I confirmed that every time the auto-start stop kicks in, the truck won't start again. Even after multiple attempts etc, I have to disconnect the battery and reset it, then it starts again. Seems like a liability to leave it like this incase someone uses my truck and accidentally turns on the auto-start stop feature.

 

[turbom5]

Great news we are learning something new as a community now. Thank you for posting @Carlos.33193. Is there any PCR fuse for your truck? I think if anything I would leave both batteries and only pull fuse F52 on the more basic trucks that have it. This would keep both batteries interconnected adding cold cranking amps and capacity. I would not recommend running them without the aux battery if you cannot disable PCR/Auto start stop. The smaller battery is there to protect the big battery during these events by carrying the load during the off portion of auto start stop. The engineers knew what they were doing and added this battery for that reason. I am not against the aux battery. I just think if enough people had issues with them, it may work for them on lower trim trucks it seems now, to take them out of the equation, but if removing them, I think it's required to disable auto start stop at that point. Otherwise what is the point.

 

[Carlos.33193]

The underhood fuse box diagram shows the F52 fuse is labeled PCR CTRL FEED, it just doesn't have a physical fuse in there. The OBD code that triggers Everytime the car goes into start stop mode is Starter 3 Relay Stuck Off.

I'm currently relying on auto start stop Eliminator, but I'm afraid in the future if it somehow fails, or I accidentally turn it back on, or someone borrows my truck it will be stranded at the first red light.

I hope the community can figure this out, because I'd love to keep the larger single H8 battery, I always did this in my previous RAMs and this is the first time I've had one with an aux battery. It just makes changing batteries out in the future much easier and helps with my inverter when I go camping.

 

[firemedic10584]

Add me to the list for completing this mod! Just finished it up on my 2026 Laramie. I went with the Ever Start H8 from Walmart for about $200. Followed the directions exactly as listed by the OP. Went for a drive and everything seems to be working just fine. Auto start/stop did not engage for me even with the AC off, which is good, I hate that feature. I did have a CEL on first start up after putting the new battery in, but I had no active codes. Likely just a low voltage CEL. I cleared it, started back up and it did not come back on. I think it's a good investment. I'll be putting my factory battery, which is new still, in my wifes tahoe since her battery is a few years old and currently an H6, but will fit an H7. So it's a win win for me!

 

[Carlos.33193]

Add me to the list for completing this mod! Just finished it up on my 2026 Laramie. I went with the Ever Start H8 from Walmart for about $200. Followed the directions exactly as listed by the OP. Went for a drive and everything seems to be working just fine. Auto start/stop did not engage for me even with the AC off, which is good, I hate that feature. I did have a CEL on first start up after putting the new battery in, but I had no active codes. Likely just a low voltage CEL. I cleared it, started back up and it did not come back on. I think it's a good investment. I'll be putting my factory battery, which is new still, in my wifes tahoe since her battery is a few years old and currently an H6, but will fit an H7. So it's a win win for me!

Did you have an F52 fuse present in your fusebox?

 

[firemedic10584]

Did you have an F52 fuse present in your fusebox?

Yes. Sorry, forgot to confirm that. I had that and removed it.

 

[firemedic10584]

Also, I just went out and checked if remote start still works after someone asked me to check that. It fired right up, and I also forgot my low fuel light is on, which typically doesn’t allow the truck to remote start when it’s low on fuel. Coincidence?

 

[Carlos.33193]

Also, I just went out and checked if remote start still works after someone asked me to check that. It fired right up, and I also forgot my low fuel light is on, which typically doesn’t allow the truck to remote start when it’s low on fuel. Coincidence?

Usually my previous RAMs would turn on, but then turn off after a little bit if a check engine or low fuel light was on.