Charging behaviour

M

MikeR

New member
I suspect that my charging system may be faulty.

The car is a 2019 P300 with 17000 miles.

I recently plugged a voltmeter into the 12v accessory port and observed the following:

At rest 12.8v -fresh off the ctek charger.

Start the engine, voltage at idle is 12.6v.

Go for a drive and the voltage varies from a high 15.0v down to 12.6v - when the voltage changes there is an audible click (or chirp) -presumably a relay.

I have a bluetooth battery monitor connected to the battery terminals which offers a charging test - it reads voltage at idle and 2,500 rpm - both are fails.

There is no indication on the dashboard that there is a charging problem.

So can anyone comment on this - is this normal or faulty behaviour?

TIA

Mike.
 
I see up to 14.8V when I'm driving so that's a "normal" charging voltage when running. If the battery has just been charged it's reasonable to assume the BMS won't need to switch on the alternator - there's nowhere for the electrons to go! If you start getting battery low warnings, even when the hazard switch light goes out after the car is locked for 10 minutes or so, then worry!
 
The stop / start battery is almost certainly an AGM (Absorbent Glass Mat) type. These things are not like the batteries of old and have very specific charging and management regimes. My 2018 XES had a non functioning stop / start system early on in it's life and a battery control module update was needed to fix it. You'll only get an accurate voltage reading with it disconnected from the car. Charging of these can be anywhere from around 14.4V - 15V. Float / maintenance needs at least 13.5V. My BCM on the XES was providing float at 12.7V before the update and 13.7 after. I can't remember the change voltage, but it also wasn't enough, basically, my battery was being held at around 80% charge. No problems at all since he BCM update. Here's hoping the new owner enjoys it as much as I did.

I'd say that if your start / stop works ok and it starts, you are probably ok. If stop / start is not working, you may well have an issue that needs fixing. Hope this helps!
 
Also 12.7V off the charger is pretty much 100% charge. What is it if you drive for a while, disconnect the battery, then measure after an hour?
 
are f type drivers just getting OCD, if it starts and drives ok what is the problem, cars need to be used and not garage queens. plugged into chargers
 
gasgas said:
are f type drivers just getting OCD, if it starts and drives ok what is the problem, cars need to be used and not garage queens. plugged into chargers
Click to expand...

I bought my F Type as a "weekend" car only to be driven on dry sunny days (winter included).

Due to the rainy summer I've not used it much this year since buying in April, but I have put some miles on it recently. I find using a battery conditioner gives me peace of mind that the car will start when I need it.
 
If the Battery is fully charged off the CTEK, then the BMS will probably decide it doesn't need charging as that's just a waste of energy (Charging isn't free)

I only put mine on the CTEK when it;s not being used for longer periods, usually in the winter when the Evoque is just more suited.
 
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