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Discussion Starter · #1 ·
Hi,

past couple of weeks my V40 D2 (1.6) 2014 (MY15) won't allow Start/stop - it says Unavailable, explanation is that battery is charging or temperature is too low (it's between 15C and 20C these days).

Past year I have been doing very low mileage due to working from home, and mainly these are short trips - I know it's not the best thing for a diesel. From time to time I get Low battery warning when I turn off the engine and Infotainment remains on. I did some longer drives last weekend (up to an hour), but no changes in availability of Start/Stop.

I changed main battery 4 years ago (currently I have AGM battery), but support battery is still factory one.

I tried to check batteries voltage, but it seems my OBD2 dongle is simple one and does not read this data (using Car Scanner on Android).

Any tips what could be the reason - support battery to be replaced, or really longer drive to charge main battery? Any suggestion for a proper OBD2 dongle that could read battery data?

Thanks,

L
 

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I had to drive to work and back an entire week before start stop became available. Every trip would be around 25 minutes long.
 

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I left my car outside in the cold this past winter for 3+ months. Came back the low battery only came on after the next couple of short trips and starts. I did take a 35-40 min trip each way on 40-50 mph roads. The journey up, drove it normally, put on about 15 miles going at speed, arrived at destination, parked up, restarted car after an hour, still showed low battery, return leg on the 40-50mph roads I used 5th Geatronic in S mode instead of 6th (so that revs are around 2k) most of the way back, low battery disappeared, didn't seem to have any mpg penalty.
 

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Discussion Starter · #5 ·
I'll give it a try with a longer trip. In meantime I ordered iCar2 Vgate to check batteries stats.

What about support battery, what happens if this battery is dead, it impacts only start/stop system, or car won't start at all?
 

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Diesels need to get to full operating temp to burn particulates. Short runs will not do this. Hence the stop start not functioning. Man factories only give 12 month warranty for cars with stop start. Same battery 3 year warranty with NO stop start. Wonder why ????? Batteries only last few years anyway. I actually turn off stop starter those launch takeoffs :)
 

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I'd look at getting a smart charger to keep your battery topped up. I've got a Noco Genius 7200 but the CTEK range is also good.
I've got a few cars so none of them get a huge amount of miles on them and as a result I need to keep them topped up via a charger. Might be worth the relatively small investment especially if you don't think you'll be doing a lot of miles in the near future.
 

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I'd look at getting a smart charger to keep your battery topped up. I've got a Noco Genius 7200 but the CTEK range is also good.
I've got a few cars so none of them get a huge amount of miles on them and as a result I need to keep them topped up via a charger. Might be worth the relatively small investment especially if you don't think you'll be doing a lot of miles in the near future.
Not much help for charging the Stop/Start battery which is buried behind the front bumper. (Unless the OP wants to take the bumper off!)
 

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Not much help for charging the Stop/Start battery which is buried behind the front bumper. (Unless the OP wants to take the bumper off!)
The auxiliary battery isn't capable of providing the power for the S/S. It is the main battery that needs the power. A tiny motorbike battery ain't going to turn a car flywheel for any period of time. All that does is keep the other electrics alive.

 

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The auxiliary battery isn't capable of providing the power for the S/S. It is the main battery that needs the power. A tiny motorbike battery ain't going to turn a car flywheel for any period of time. All that does is keep the other electrics alive.
The "tiny motorbike battery" is the one that supports the start/stop function. The support battery can still provide 170A for short periods of time (more than enough to restart a warm engine) If the main battery were sufficient why do cars with start/stop need two?
 

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Correct explanation is in the above link quoted by MartynT:

The dual battery system isolates all power supply sensitive electrical components which may be affected by low voltage from the primary battery during the engine starting phase.

Two contact switches are used to change the power supply into two separate circuits when an engine start is required.

Electrical power is then supplied to the sensitive electrical components from the secondary battery when an engine start is in progress.

The primary battery supplies power to the starter motor and maintains essential power to the Engine Management System (EMS) which is essential for engine starting.

Primary and secondary battery voltages are monitored to ensure sufficient voltage is available for the next start event and charge can be supplied to the secondary battery when required.
 
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