Start/Stop with Brake feature not working - Jeep Compass Forum
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post #1 of 10 Old 10-17-2018, 01:57 AM Thread Starter
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Start/Stop with Brake feature not working

Purchased my 2018 Compass Latitude, brand new, this past May/June. For the last couple days, the display says the Start/Stop feature isn’t ready because the battery is charging. The battery is at 14.5V. What should it be at?
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post #2 of 10 Old 10-17-2018, 08:25 AM
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Bad Battery need to update computer
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post #3 of 10 Old 10-17-2018, 05:34 PM
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could be the secondary batter, i have heard they have one

dealer time
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post #4 of 10 Old 10-17-2018, 06:19 PM
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Quote:
Originally Posted by mdram4x4 View Post
could be the secondary batter, i have heard they have one

dealer time
I agree. I think the information display shows the voltage value for the main battery while the battery start/stop diagnostic talks about is the auxiliary battery.
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post #5 of 10 Old 10-18-2018, 12:26 PM
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Originally Posted by Reesh
The battery is at 14.5V. What should it be at?
14.5v tells me you looked at it with the engine running, which tells you only that your alternator is working. Have to turn the motor off to find out what the primary battery level is, best to check in the morning before starting the car. Checking it right after it has been driven may give a high reading since it was just charging right up until your shut it off.

As others said, secondary battery you don't know the voltage from the dash you would need to check it with a multimeter. Mine used to give me messages like that too and I brought it in (its under warranty so why waste my time troubleshooting it for them), they insisted both batteries tested OK but that was the same time that we got into the other issues I was having and they replaced my BCM. I never use the autostop so may still be ongoing for me but I don't really care as long as no warning lights on my dash.

Could be a flunky IBS (that stands for "Intelligent Battery Sensor", it is anything but...) in which case there is pretty much nothing to do but bring it in and let them diagnose it. FCA has made what should be a simple system into something way over-complicated so as long as its in warranty don't bother. It will just make you angry (I seriously can't think of anything stupider than putting a tiny battery next to a medium battery side-by-side when one large battery would have done just fine...)
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post #6 of 10 Old 10-18-2018, 06:23 PM
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I seriously can't think of anything stupider than putting a tiny battery next to a medium battery side-by-side when one large battery would have done just fine...
Lol yeah that is some basic designing error. The single most important factor for any engineering project it to built something with fewest pieces/components possible. So if something could be designed with a single battery, instead of two, single should have been the way to go.

Now we end up with a system that is composed of two batteries and a diagnostics pipeline that requires both batteries to function @100% for certain systems to work properly, while you can only actively monitor one as the driver. There is also the intrinsic limitations of having two different sized batteries on a single circuit(unless both batteries have their own alternator). If one battery goes bad, it will reduce the charging efficiency of the second "healthy" battery, as the charge will leak from the bad one.
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post #7 of 10 Old 10-18-2018, 09:05 PM
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Quote:
Originally Posted by Tripod
There is also the intrinsic limitations of having two different sized batteries on a single circuit(unless both batteries have their own alternator). If one battery goes bad, it will reduce the charging efficiency of the second "healthy" battery, as the charge will leak from the bad one.
There is only one alternator of course. The batteries are not directly connected, charge current to the smaller battery is regulated based on its state and isolated completely at times ("state" being sensed by the so called "Intelligent Battery Sensor"). I think this came to be the way it is in our vehicles for one or both of the following reasons:

1) In other FCA cars with ESS that came before this car the second battery was not in the engine bay, apparently due to space constraints. I imagine they more or less "copy-and-pasted" the existing ESS design for this car but found they had plenty of room for placing both batteries in one location, but choose to still use the two battery design to avoid engineering costs of re-designing and testing.

2) Two smaller, lower quality batteries are possibly cheaper than one large battery that meets all the specifications served by the two individual batteries.

As a team, if properly implemented and playing to their strengths, the two battery system can probably perform as good or better than a single really expensive battery for a longer period of time. As the primary battery ages, its capacity diminishes as well as its ability to maintain desired voltage under heavy load (ie, cranking the starter in cold weather). The electronics do not appreciate big voltage dips, they can potentially use some capacitors and voltage regulation to continue normal operation throughout a range of input voltage but at some point if the voltage is too low (say, dropping to 8.5 volts while the starter is cranking for 3-10 seconds) it will cause things to go haywire. Thats where having a small isolated battery that can maintain 12.x volts to the electronics at low amperage keeps that side happy while the primary battery swings wildly on startup between whatever its voltage dips too during cranking (10 or 11 volts for a somewhat aged battery) and then bouncing up to 14-18 charging volts as the alternator spins up.

Still, one really high quality large battery could maintain 12 volts while under a heavy load for most of its life I would think. A really big capacitor would be better in place of the secondary battery but that would be much, much more expensive than a cheap little SLA. It all comes down to cost I'm sure.
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post #8 of 10 Old 10-24-2018, 06:33 AM
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I just got my 2018 compass trailhawk back from the dealership for this same reason. They replaced the battery and a sensor, but it seems like it’s still having the same issue. The screen also keeps saying “battery charging”. This is the second time I have to take it in for electrical issues.
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post #9 of 10 Old 11-03-2018, 04:44 AM Thread Starter
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Hello all,
Thanks for the input and advice! I brought it to the dealer for a recall relating to the brake system and it seems that the start/stop feature has been rectified!
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post #10 of 10 Old 11-16-2018, 12:57 AM
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Just got mine back from the dealership (warranty covered it plus rental). They said they could not get a factory secondary battery, so they have contacted corporate to authorize the use of an aftermarket battery. We'll see how it goes.

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