Battery Health (P3 and onwards)

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Having recently seen quite a few owners mentioning that their car seems to think the battery is always at a low state of charge (even after replacing the battery) .

I thought I could shed some light on the subject (always ensure your alienator and battery are indeed in a good state of health).

Luckily, I had a perfect test subject on my driveway (2012 xc70). Despite having a new 100AH battery it would quickly complain of low battery when sat without the engine on listening to the radio, despite voltage never getting lower than 12.5V ….hmmm

If your car is fitted with a battery monitoring system, it should be reset and calibrated after the battery is changed, and i had never bothered.

But before resetting I wanted to know what the car believed its “idle” current usage was using VIDA. It seems, over the years it had decided that it takes 100mah to just sit still and do nothing when “Readout of current from battery monitoring sensor shows” it is more like 15mah with the ignition on. So you can see it’s calculating that it can’t run for long without risking getting to low too start the engine.

I then used “Readout of information stand-by current” to reset the Standby calculator (it then takes takes between 4-6hrs to calibrate with the car left locked and “off” and adopts 30mah as a baseline see picture).

Then “Resetting the information to zero on power supply when replacing the battery” was used to reset all other aspects of the cars battery monitoring to zero.

Happy days, it will now run much longer without complaining that the battery is low.

By the way , you can also reset the BMS by unplugging it from the battery whilst the engine is running or using the “in car method” like so :-

• 1. Switch on ignition to position 2 (long press without starting the engine)
• 2. Switch to dipped beam
• 3. Turn the rear fog lights on 3 times (that’s 6 presses)
• 4. Turn the hazards lights on and off 2 times (that’s 4 presses)
• 5. Then the battery symbol in the speedometer should flash 3x quickly.
• Its best to leave the car alone for at least 5 hours afterwards