Cold weather, no remote start, aux batt delete

[\/\/0j0]

2021 Diesel Rubicon

Duracell 94r H7 AGM 85cca battery installed ~2 months ago
Aux battery deleted at same time
Fuse 42 pulled
Running a tazer JL mini.

All was well until today when it was 8F outside. Remote start failed to start truck twice. One honk and no attempt to crank. Got in and it cranked right up. In dash volt meter showed 12.2 to start before slowly(10-15 min) rising up to 14.2 before I stopped paying attention while driving.

Any ideas on root cause? Not having remote start when it's most needed is not convenient.

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[NC_Overland]

12.2 volts probably. That’s low.

 

[\/\/0j0]

12.2 volts probably. That’s low.

I, too, thought it was a bit low. I had no problem remote starting it yesterday. Temp was 25F and I started it twice and let it run to de ice it. No issues. That's why it surprised me today. Is it possible it took more to crank twice than it charged in 30 minutes of running?

 

[Dave D]

Was your fuel level low.
Mine wont remote start with low fuel.

 

[\/\/0j0]

Was your fuel level low.
Mine wont remote start with low fuel.

That is an interesting data point. I'll store that away for future troubleshooting. But in this case my fuel gage showed >3/4 so probably wasn't it.

As an update, overall, after my 35 mile round-trip commute yesterday, the truck remote started without issue today. It timed out and when I got in and started it, voltmeter showed 11.6 before climbing quickly to 12.6 at idle and 14.2 while driving.

 

[JTdiRtyD]

This seems to be a common thing popping up lately. I think it's pointing to the charging system not getting batteries back to full when it's cold out, and the BMS tolerance is set too high during remote starts and it thinks the battery is too weak so it cancels the start.

I have a brand new Duracell AGM, tested good and fully charged before install. Aux battery removed. I've seen battery readings gradually decrease to around 12.5-12.7 volts over a week or so of just driving to work and back, 20 miles each way, but when I have longer trips the battery gets back to 13.2 and remote start works fine every time. I'm going to start leaving the truck on a Noco overnight during the week and see if this resolves the issue.

from my understanding, the smart battery system doesn't put a good charge until it sees a 20% loss, and I'm guessing when it's cold enough to affect AGM amps the charging system struggles to catch up. It's enough to keep the vehicle running and all systems happy which is why it appears fine otherwise, just not enough for remote start checks.

I' also contemplating tossing my 2nd Renogy monitor to see what amps are sitting at after each commute.

 

[NC_Overland]

The fuel level has to be low enough for the low fuel light to be on for remote start to not work.

 

[\/\/0j0]

This seems to be a common thing popping up lately. I think it's pointing to the charging system not getting batteries back to full when it's cold out, and the BMS tolerance is set too high during remote starts and it thinks the battery is too weak so it cancels the start.

I have a brand new Duracell AGM, tested good and fully charged before install. Aux battery removed. I've seen battery readings gradually decrease to around 12.5-12.7 volts over a week or so of just driving to work and back, 20 miles each way, but when I have longer trips the battery gets back to 13.2 and remote start works fine every time. I'm going to start leaving the truck on a Noco overnight during the week and see if this resolves the issue.

from my understanding, the smart battery system doesn't put a good charge until it sees a 20% loss, and I'm guessing when it's cold enough to affect AGM amps the charging system struggles to catch up. It's enough to keep the vehicle running and all systems happy which is why it appears fine otherwise, just not enough for remote start checks.

I' also contemplating tossing my 2nd Renogy monitor to see what amps are sitting at after each commute.

This is all good info. Thank you for the reply.

I hate when "smart" means too complicated to work in real world conditions. I don't want to be the old man yelling at clouds over here but this is a system that was figured out long ago and worked fine until all of this ESS and dual battery business entered the scene. It's frustrating that manufacturers keep trying to fix things that weren't broke.

I appreciate your insight and look forward to any additional data points that you capture. Maybe I'll need to figure out some type of battery tender to install along with a block heater, whenever I get around to it, so that I can have the perfect remote start on the dozen or so mornings a year that we have temperatures that dip into single digits.

 

[DylanM]

I hate when "smart" means too complicated to work in real world conditions. I don't want to be the old man yelling at clouds over here but this is a system that was figured out long ago and worked fine until all of this ESS and dual battery business entered the scene. It's frustrating that manufacturers keep trying to fix things that weren't broke.

It's not so much that manufacturers are purposely trying to fix things that weren't broken, they've been having to implement all these little tricks to try to improve fuel mileage due to CAFE standards. While it may seem stupid to overcomplicate systems that worked perfectly fine previously as they were, the changes generally do make small improvements to efficiency, and when you add up all those little improvements they can literally mean the difference between a vehicle meeting the CAFE standards versus not meeting those standards. When they didn't meet CAFE standards the manufacturer paid penalties.

The other part of the equation is the consumer keeps demanding more power, more features, more room, etc, which all tends to lead to higher weight and fuel consumption. It's a balancing act to try to give the consumer what they want while also complying with government standards to keep from getting fined, all while still trying to make some profit without hiking the prices so high that nobody will buy.

 

[\/\/0j0]

It's not so much that manufacturers are purposely trying to fix things that weren't broken, they've been having to implement all these little tricks to try to improve fuel mileage due to CAFE standards. While it may seem stupid to overcomplicate systems that worked perfectly fine previously as they were, the changes generally do make small improvements to efficiency, and when you add up all those little improvements they can literally mean the difference between a vehicle meeting the CAFE standards versus not meeting those standards. When they didn't meet CAFE standards the manufacturer paid penalties.

The other part of the equation is the consumer keeps demanding more power, more features, more room, etc, which all tends to lead to higher weight and fuel consumption. It's a balancing act to try to give the consumer what they want while also complying with government standards to keep from getting fined, all while still trying to make some profit without hiking the prices so high that nobody will buy.

An excellent reply! Thank you for pointing this out. I was overly simplistic in my assessment and acknowledged the effect while forgetting the cause. You are very much correct about overzealous regulations leading to complex and expensive compromises.

I believe your second argument points back to the root cause of the first and illustrates why components of less than the highest quality may be chosen to achieve the balance between up front affordability and compliance with regulatory guidance.

I suppose this leads into the age old questions of how much is too much regulation and at what point do we bump into the law of diminishing return in terms of cost and benefit?

 

[JTdiRtyD]

I wasn't thinking clearly in my reply above, so I'll clarify here. I also posted this in another thread regarding failed starts.


Didn't take long after installing a new battery and mine was failing remote starts again. Remote start works great when it's warm out, and for the first couple weeks it was plenty warm so I had assumed the battery had resolved it, but now that this polar vortex crap is here I'm seeing failed starts again. New battery was tested good and normal starts show zero sign of a weak battery.

I think it has to do with two things, the smart BMS and short commutes. I had read somewhere that the charging system doesn't really charge unless it sees the battery drop below "x" %, instead it just maintains, and you need longer commutes before it will actually put a good charge back in.

I'll start off by stating this following about 12v batteries:

Fully charged = 12.6-12.8 volts
Charged (good) = 12.4 - 12.6 volts
Needs charging = 12.2 - 12.4 volts
Weak = 12.0-12.2 volts
Bad = less than 12 volts

After charging my battery to 100% I'll see mid-high 12's voltage before starting the engine. My commute to work is 20 miles each way, and after a week or so of going to work and short trips into town, my voltage levels out to around 12.4-12.6 volts. Then I drive 2 hours to the fish house and I see my battery back into the fully charged range, 12.6 - 12.8 volts. After getting back home and commuting to work I'll see it level back out around 12.4-12.6 volts. A "good" battery according to the BMS, so my assumption is it's not prioritizing a charge, but just monitoring and maintaining

When remote start fails, it hits the starter and then immediately cancels the start. When I get in the truck after a failed start and watch the voltage, it will bein that 12.4-12.6 range and then dip into low 11's/high 10's for a second as the starter engages, then promptly jumping to mid 13's when the engine starts.

All that to say this, I think the reason our remote start fails when it's cold is the BMS during remote start operations has too high of an allowed voltage tolerance. The BMS aims to keep the battery around the mid 12's. Cold weather decreases battery output, even in a brand new battery, and during remote start operations the dip in voltage during starter engagement drops below the accepted tolerance, so it cancels the start. During the summer the battery output isn't affected, so the dip isn't as big and doesn't cancel the start. This is exaggerated with aux battery deletes (or low/old/bad aux batteries), because the aux battery was enough supplemental amps that cold weather starts didn't dip numbers low enough.

How to fix this? Run a battery maintainer (trickle charger) at night.

 

[Y-Guy]

How to fix this? Run a battery maintainer (trickle charger) at night.

That's what I do. Started it a year ago with my 2020 Gladiator as starting was becoming belabored and I figured it would get me through the winter before I tackled replacing the batteries. Worked so well I kept doing it and now do it once a week with both my 2025 Gladiator and my wife's 2024 Wrangler. Here is what I use. Here is a thread on the subject.

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