992 wild battery voltage fluctuations - Page 1 - 911/Carrera GT - PistonHeads UK

Has anyone ever seen anything like this? https://youtu.be/LWgu71ePrko?si=AlO3vODwTwBYqTxq Picked the car up yesterday from a private buyer. 2019 Carrera S 17k miles Brand new OEM battery was put on the car 3 days ago Despite the weird battery fluctuations the actually runs fine without and warning lights on the dash. The Battery did start at 14v at the start of the journey. When you start it now it says stop start unavailable and the volts are 9-10. Any clues?

I would start with looking at the terminals and surround cables for loose connections, given it's just been messed with this is your most likely bet. 14V is fine as is the pull down to 9V during crank but it should recover to whatever the alternator is supplying thereafter. The video won't load, says its private, but assuming you're seeing these values on the dash and not a multimeter you're likely getting a filtered and potentially lagged view w.r.t to what is actually going on. I would check all the connections, tighten anything loose, lock the car and let it sleep for 30 minutes then turn it back on and check. HTH

That’s really odd. I’ve never soon such fluctuations with my battery voltage. It’s always in the 12-14v range.

Get a multimeter onto the battery (or even better, a victron smartbatterysense https://www.12voltplanet.co.uk/victron-smart-batte... that datalogs battery voltage and go from there. Could be a loose connection, my 981 battery sits between 12.4 and 12.8v if not used for a while, been 13.4V and 15.4v when driving. 9V to 10v, if true, would be a problem and indicate alternator issues and will cause misfires due to low ignition voltage Victron smartbatterysense output like this

Apologies, the video should now be fully public: https://youtube.com/shorts/LWgu71ePrko?feature=sha...

Turning the car on this morning and the display is reading that the battery is dead flat. Indicator is red etc. The car starts and runs fine however. No warning lights on the dash. BTW, Porsche fed back on email saying that it looks like a battery sensor issue, but it will need to be checked. This can happen if the 12 V battery is not maintained correctly (charging directly on the battery rather than the specific charge points). "Unless the car is displaying a specific warning I don’t think it’s an urgent concern"

Wow. Definitely not normal. Loose connection somewhere? Is it under warranty? If so, show video to dealer Does it happen when car is at idle or only when the car is moving / vibrating? can you get a multimeter onto the battery to see if it is happening at the battery terminals and replicate on a multimeter?

If that was valid reading I'd expect the car to exhibit numerous related faults. As said above check the terminal connections on to the battery. There's a connector on the negative terminal which the car uses for battery sensing. Check it is correctly clipped together and no wires have been pulled out of it during the recently battery change, they are small guage red + white wires and quite vulnerable. Edited by M11rph on Wednesday 10th April 12:17

elan362 said: Get a multimeter onto the battery (or even better, a victron smartbatterysense https://www.12voltplanet.co.uk/victron-smart-batte... that datalogs battery voltage and go from there. Could be a loose connection, my 981 battery sits between 12.4 and 12.8v if not used for a while, been 13.4V and 15.4v when driving. 9V to 10v, if true, would be a problem and indicate alternator issues and will cause misfires due to low ignition voltage Victron smartbatterysense output like this That's pretty cool and I assume easily transferrable to another car? Is there anything else to get other than the unit, a bit of cable and d/l the app?

Yes, it just connect to the battery terminals. Sticks onto the battery with a stick 3M tape. It is Easy to move between batteries / cars. Knowing the battery temperature is important for charging lithium batteries. You should not charge them below 0c. ( Not relevant for my 981) but I've one in my Motorhome, and the SBS communicates with my victron solar setup to prevent low temp charging. One of the benefits in the Car is I can monitor the battery charge from the house and don't need to unlock the car @ wake it up to get a voltage reading. The victron App is free to download. That's all you need

Found it!! The battery sensor plug that you pointed out above on the right side battery terminal was fine but there is a small wire on the other side of the battery that completes the circuit and provides the reading to the dash in the car. The one on the left, single red wire + 8mm nut was loose. That sorted it it! Thank you guys, very much appreciate the support

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Glad you got it sorted OP

Glad it was a simple OPC-free fix. Thanks for updating the thread.