battery warranty

[Ascotmacan]

The battery in my 2 year old Macan does not seem to be holding its charge very well. During driving it is being charged well up to 14.7 volts but when parked at home the voltage drops to less than 12 volts in a few days. I believe Porsche did not use to warranty batteries longer than about 12 months but my warranty documents do not mention any timescales. Any experiences?

[andreas]

Most batteries you can buy from Halfords have a 4 or 5-year warranty, so I can't see how Porsche can decline a warranty claim on a failed 2 year old battery.

[GWL]

I may be corrected on this, but I believe the 14.7 volts is a "charging" voltage supplied by the alternator ( In order to charge the battery, the applied charging voltage has to be higher than the battery's nominal 12 volts in order to "push power" into the battery).

However, when the car is sitting with the engine off (i.e. no charging voltage from the alternator) then it will just show its rated 12v (or slightly lower as there are still systems drawing power even when the car is standing) .

Hence I don't think there's a problem.

Same sort of thing applies to rechargeable batteries you may use at home. They are, say, 1.5v but the charger will apply, say, 1.75v to them to charge them. However, once charged and removed from the charger, they will provide their nominal 1.5v

[pmg]

I may be corrected on this, but I believe the 14.7 volts is a "charging" voltage supplied by the alternator ( In order to charge the battery, the applied charging voltage has to be higher than the battery's nominal 12 volts in order to "push power" into the battery).

However, when the car is sitting with the engine off (i.e. no charging voltage from the alternator) then it will just show its rated 12v (or slightly lower as there are still systems drawing power even when the car is standing) .

Hence I don't think there's a problem.

Same sort of thing applies to rechargeable batteries you may use at home. They are, say, 1.5v but the charger will apply, say, 1.75v to them to charge them. However, once charged and removed from the charger, they will provide their nominal 1.5v

Agreed, I suspect no long term issue, especial;;y if it is accepting charge whilst driving.

I find with modern battery protection systems and the drainage on a battery when vehicle left, it is best vehicle left on the likes of a CTEK charger if not to be used for a few days

[Nuclear Nick]

This is normal, the battery is fine. No-load voltage will drop over a few days, into the 11 to 12 volts range while background electrical systems are operating, however the ECU will gradually shut down non essential systems in order to protect the battery capacity and maintain enough power to start the car. Standing no-load voltage is not an indication of remaining battery capacity. During this time a message may appear on the PCM screen that battery protection is operating and advising to start and run the car to recharge the battery.

[Neil1911]

After being parked for 10 days at the airport no such message was apparent on mine. I didn't think to look at the voltage, next time maybe....

[Alfanut]

The battery in my 2 year old Macan does not seem to be holding its charge very well. During driving it is being charged well up to 14.7 volts but when parked at home the voltage drops to less than 12 volts in a few days. I believe Porsche did not use to warranty batteries longer than about 12 months but my warranty documents do not mention any timescales. Any experiences?

Correct, it’s not holding its charge very well or something is taking excess current when the car is lying idle (dash cam, immobiliser???). As others have said you can’t really tell the full health of a battery by simply checking the no-load voltage. However, for the battery to fall below 12v in just a few days, which is equates to about 50% discharged, does sound like it’s well past its best. It almost sounds like it’s previously had a deep discharge, with AGM batteries particularly that’s the beginning of the end.
Does the stop start function still operate? If the battery is weak the car will restart after only a few seconds as the voltage will have dropped to the starting threshold. Let us know how you get on with the warranty.

[Nuclear Nick]

The battery in my 2 year old Macan does not seem to be holding its charge very well. During driving it is being charged well up to 14.7 volts but when parked at home the voltage drops to less than 12 volts in a few days. I believe Porsche did not use to warranty batteries longer than about 12 months but my warranty documents do not mention any timescales. Any experiences?

Correct, it’s not holding its charge very well or something is taking excess current when the car is lying idle (dash cam, immobiliser???). As others have said you can’t really tell the full health of a battery by simply checking the no-load voltage. However, for the battery to fall below 12v in just a few days, which is equates to about 50% discharged, does sound like it’s well past its best. It almost sounds like it’s previously had a deep discharge, with AGM batteries particularly that’s the beginning of the end.
Does the stop start function still operate? If the battery is weak the car will restart after only a few seconds as the voltage will have dropped to the starting threshold. Let us know how you get on with the warranty.

How did you arrive at the ‘50% discharged’ figure?

[Alfanut]

Some manufactures publish discharge tables but in general the discharge rate is a pretty steady and gentle slope between 12.8V down to around 12V which is roughly 50% of the capacity used on a lead acid battery. Beyond this things start to drop off rather quickly. There are a number of factors involved, current draw, temperature, etc.
Google “agm battery discharge chart” for some more info, for example :-

[pmg]

Some manufactures publish discharge tables but in general the discharge rate is a pretty steady and gentle slope between 12.8V down to around 12V which is roughly 50% of the capacity used on a lead acid battery. Beyond this things start to drop off rather quickly. There are a number of factors involved, current draw, temperature, etc.
Google “agm battery discharge chart” for some more info, for example :-
IMG_1454.jpeg

fascinating.

The graph after 120 hrs/ 5 days confirms the wisdom of leaving an AGM battery on the likes of a CTEK charger if left for any time