Disconnecting Negative Battery Sensor

[Bailes1992]

I understand lots of cars will be different. But what generally is the default mode in cars with smart charging if the battery sensor is disconnected?

Context...

My Duster leaves the battery in varying states of charge. When you start up the car it will charge at 14.8v for a period of time that could be 10 minutes or 30 minutes. Then once (I assume) it detects the battery is of a satisfactory charge level it will drop down to 12.8v. Then whenever you coast it will ramp up to 14.8v again until you get back on the throttle and it'll modulate back down to 12.8v again.

When the engine is turned off the battery can settle anywhere from 12.8v to 12.1v. If the car is turned off with the battery sat at 12.1v and left for a few days this can easily drop down below 12v.

I must add that the car has never failed to start, even when the battery has been down at 11.6v, it's warmed the glowplugs up and started without a fuss.

I just dislike having the battery at such low states of charge.

I put a Noco Genius 1 on it Friday night as it was reading 12.2v after the engine had been shut down and it took from 7pm Friday night to 4pm yesterday (Monday) afternoon before the charger went into 'maintenance' mode (i.e. the battery was 'full).

I'm wondering if disconnecting the sensor is likely to disable the smart charge system and maintain a constant ~14.5v or so and maintain the AGM battery at a higher state of charge? Ideally without triggering any warning lights or errors.

 

[eljefino]

Well you could try it and put it back if you're unhappy.

Other scenarios could be a compromise voltage like 13.8V all the time, or 20% load on the alternator regardless of demand.

I do expect warning lights of some sort.

The best solution is probably an aftermarket tune if they make them for your car.

Is there any situation where you'll get full voltage like weather below a certain temperature, AC, or headlights on?

 

[Chris142]

Im sure that disconnecting somthing that important will trigger a CEL.

 

[zzyzzx]

Try it and report back. Supposedly this is one of the ways to disable smart charging on Fords without having to press the button every single time. Also report back if it disables stop start.

 

[wpod]

Im sure that disconnecting somthing that important will trigger a CEL.

That is the engine is running light.

 

[SC Maintenance]

Im sure that disconnecting somthing that important will trigger a CEL.

My Nissan stores a code - I forget which - but doesn’t trigger a CEL. Weird I know. I found it when looking for something else. Cleared it and it never came back?

 

[Kira]

Did the Duster come with an AGM battery?

An AGM charger drops the voltage down when you approach "fully charged". I've read leaving an old style charger on an AGM overnight hurts them.

The Genius 1 doesn't have an AGM setting.
Its brain may be knocking the charging output down because it thinks it's connected to a lead/acid battery.
I didn't commit everything I read to memory but I do know a proper AGM charging profile is different.
This could be effecting you.

I bought a Genius 10 as it has an AGM setting....even though we've no AGM batteries in the family....yet.

 

[Bailes1992]

Did the Duster come with an AGM battery?

An AGM charger drops the voltage down when you approach "fully charged". I've read leaving an old style charger on an AGM overnight hurts them.

The Genius 1 doesn't have an AGM setting.
Its brain may be knocking the charging output down because it thinks it's connected to a lead/acid battery.
I didn't commit everything I read to memory but I do know a proper AGM charging profile is different.
This could be effecting you.

I bought a Genius 10 as it has an AGM setting....even though we've no AGM batteries in the family....yet.

It is an AGM battery and my Noco Genius 1 most certainly has an AGM setting. It has 4 options for 12v Lead Acid, 12v AGM, 12v Lithium or 6v Lead Acid.

I bought it to maintain the battery on our Classic Mini.

One of my concerns was the effect on the battery having a constant 14.5v on it.

 

[Kira]

Ahh...I went to a brief instructional video out of curiosity and I saw the 4 square lights but couldn't see 'em clearly.

The guideline for lead/acid batteries was that after an overnight, a battery in a car with a good charging system which read <12.2v was a failed battery. My 6 year old truck battery read 10.6v and it too started just fine. I replaced it,

If nothing else, measure your voltage every morning and see if any pattern emerges.
Maybe join a Duster forum and see if your experiences are common.

Is your battery original to the car?

 

[Bailes1992]

So I disconnected the sensor yesterday afternoon and I've done 3 ~50mile journeys since.

The alternator sits at a constant 14.6v while the engine is running and the battery is always sat at 12.8v on shutdown. The start/stop disable button is permanently illuminated which isn't an issue as I automatically turn it off anyway. But unfortunately I get a message on the dash saying "Check Start/Stop".

I am wondering if I have an excessive parasitic draw. Last night I parked up at 12.8v and this morning it was sat at 12.3v. Is that excessive? I don't know. I think I'll do a parasitic draw measurement tonight and report my findings.

 

[SC Maintenance]

Sounds like bad battery or parasitic draw.

 

[Davejam]

A battery will read higher immediately after its been charging. The 12.8 after parking isn't real.
Also could be weather/Temperature dependent.

 

[Craig in Canada]

My vehicle has a similar charge management system (2011 BMW). Its "goal" is 80% SOC, above that it behaves similar to what's described - float voltage in the low 13s unless coasting when it will go to 14.8V if the car is coded for an AGM battery (which is default after a certain year of manufacture).

OP is losing sleep over both voltage too low and voltage too high (doesn't like how either the car or the NOCO treat the battery). Here's my 2 cents, which is near worthless.

I have a CTEK MXS 5.0 wall mounted beside the car. I plug it in overnight from "time to time" which varies based on usage and weather. My battery is a 2015 dealer warranty replacement (so nothing special) and still tests around 70-80% SOH with a Solar BA9. The CTEK does not have a "constant 14.5V on it". In phase 4 it brings it up to ~14.8V and then proceeds to maintain, the specific voltage of which varies based on temperature sensed by the unit.

IMO - you seem to have power available beside the car. Get a maintainer with an AGM mode and charge current of 4-5A (e.g. CTEK MXS 5.0 or NOCO Genius 5) and use the quick-connect system to "plug it in from time to time". Don't modify the car and stop worrying about it. The system which you dislike is also monitoring the state of charge to ensure that the vehicle will always start. At the risk of jinxing myself, I couldn't expect more from my battery's service life which is 9 years old and still counting. It's never struggled to start the engine in any conditions, including over 60s of cranking at full compression (in 6 10s shifts with a short cooldown rests) to prime the oil system after a repair procedure.

EDIT: connect your charger at some point in the system other than at the battery, otherwise the vehicle's battery/energy monitoring system will not capture the charging activity properly. On BMWs the battery is in the trunk, so the recommendation is to use the jump terminals under the hood for charging.