981 flat battery - advice sought

[stewieyan]

Thanks all!

So I called AA - a very knowledgeable and friendly chap arrived, powered the bonnet, checked the battery and said it might need replacement.
I've kept the running for 20 minutes. It does work now although getting a 'steering support limited' error on the dash - but I heard this disappears.
I'm not sure if the battery actually needs replacement (unless of course it stops working again). Any good way to check that?

[ATM]

I've swapped the battery in my 981 several times with other batteries I just had lying around. The original Banner battery was in my BMW for around the last 3 months or more. It has been back in my 981 for just over a week and is working fine. I have never reprogrammed the ECU for anything. It is just a battery. It isn't that complicated. I will say I am impressed the Banner battery has lasted so well. I can't be certain it is the original battery because I have only owned the car for 6 or 7 years. In that time it has been found flat through my mistreatment many times and always recovered fine. It should have died a long time ago but it refuses to give up.

And yes if the battery is dead you can use the key blade to open the door. It isn't intuitive. You need to turn the key to activate the door handle. Remember when you open the door with no battery that the window will not drop. Bear this in mind because you can not then close the door as the window will sit outside the roof. So if you do use the emergency procedure to open the door then make sure you can get into the frunk and get the electricity restored because you do not want to leave the car outside with the door ajar or partially closed with the glass outside the roof seal.

Positive does go on the pull out from the fuse box. I use the door latch striker for negative. Then yes only the bonnet release button on the door sill will operate.

[981Boxess]

ATM said:

I've swapped the battery in my 981 several times with other batteries I just had lying around. The original Banner battery was in my BMW for around the last 3 months or more. It has been back in my 981 for just over a week and is working fine. I have never reprogrammed the ECU for anything. It is just a battery. It isn't that complicated.

Yes all batteries are the same, once the cables reach and the bonnet shuts they are all the same

No idea why they make more than one really.

[ChrisW.]

I've owned my GT4 from new in 2015. As a preventative measure I recently replaced this with the best quality battery from Tayna ... easy to do.

My original battery had a date stamped into the top of one of the terminals ...

[Panamax]

981Boxess said:

Yes all batteries are the same, once the cables reach and the bonnet shuts they are all the same. No idea why they make more than one really.

Tongue firmly in cheek. Back in the day the cowboys would make a battery that looked like the real thing but the expensive bits, the metal plates inside, would be of poor quality and simply physically smaller (shorter) than the plates of a decent battery. Looked the same but wasn't. Same as tyres; they're all black and round so there can't be any difference - can there?

Tayna is your friend. Buy identical specification, install it yourself and don't bother with coding.

[ATM]

I'm a bit more selective with tyres. But a battery is just there to start the engine - assuming you turn off that stop start rubbish. So you either get a big one which is heavy but won't go flat as quick whentje car is left unused. Or you get a smaller one which is lighter but sill go flat quicker. I've recently been experimenting with a teeny tiny LiFePo4 battery in my 996 and 986. I was planning to try one in the 981 too but just haven't gotten round to it yet.

[ChrisW.]

I think the car would need to know if a battery with a different charging and fully charged voltage was to be fitted ... that's why Li batteries use a different charger from Lead/Acid/ Gel/ AGM etc ??

[ATM]

But back to standard lead batteries I don't understand why the car needs reprogramming. Most modern car chargers will just charge any [lead] battery. So why is a Porsche different.

I've had my little LiFePo4 now over 2 years. And it's been great. I don't have a special charger for it. These either have charge or they do not. So just having a little bit of charge will get the engine started and then it will charge off the engine. I have not put it on my 981 because the complicated more modern car does scare me a bit.

I believe they all have a little circuit board inside which fools the outside world into thinking they are an old fashioned battery. So if it needs charge it will show a lower voltage and then when it's full it will show a higher voltage. The better ones will just turn off if the charge gets too low to prevent damage from being fully drained. This happened to me when driving the 996 with a duff alternator and it wasn't pleasant. So in theory you can treat them like st and they should be fine.

I believe the only standard chargers which can damage a LiFePo4 are the ones which have a fancy recovery mode for very low voltage or dead batteries which pulse the charge on and off quickly to help revive an old fashioned battery. I think this is an outdated concept nowadays with AGM but I'm not an expert by any stretch. Plus the LiFePo4 should never show a really low voltage like that.

[981Boxess]

ATM said:

But back to standard lead batteries I don't understand why the car needs reprogramming. Most modern car chargers will just charge any [lead] battery. So why is a Porsche different.

Not sure where you are getting that from, not sure anyone is suggesting that?

One thing is for sure with AGM batteries and alternators that can charge different ways the days of lobbing a similar battery on a modern car and walking away are long gone. There is a little more to it than that today.

[Armitage.Shanks]

981Boxess said:

One thing is for sure with AGM batteries and alternators that can charge different ways the days of lobbing a similar battery on a modern car and walking away are long gone. There is a little more to it than that today.

Agreed but I would expect the alternator to 'undertsand' the current charge state of the battery by reading the voltage to adapt to a charging regime. It can't be any more complicated than that? My guess is the 'coding' is only to record a battery into the car history for when a main dealer hooks it up to scan?

In my 981 and now 718 the voltmeter when the endgine is running regularly peaks as high as 15.0v (settling to around 14.6 and then will sometimes drop back to 13.9v).

I've always questioned that 14v+ seems a high rate of charge, but that seems the norm.

[981Boxess]

Armitage.Shanks said:

981Boxess said:

One thing is for sure with AGM batteries and alternators that can charge different ways the days of lobbing a similar battery on a modern car and walking away are long gone. There is a little more to it than that today.

Agreed but I would expect the alternator to 'undertsand' the current charge state of the battery by reading the voltage to adapt to a charging regime. It can't be any more complicated than that? My guess is the 'coding' is only to record a battery into the car history for when a main dealer hooks it up to scan?

In my 981 and now 718 the voltmeter when the endgine is running regularly peaks as high as 15.0v (settling to around 14.6 and then will sometimes drop back to 13.9v).

I've always questioned that 14v+ seems a high rate of charge, but that seems the norm.

Fair enough - if your battery goes you will know exactly what to do and save yourself a few quid in the process.

[Panamax]

Armitage.Shanks said:

I've always questioned that 14v+ seems a high rate of charge, but that seems the norm.

Car battery isn't a 12v battery, it's about a 12.7v battery, so you're going to need around 14v to charge it.

Typical charging voltage is in the range 13.6 to 14.7 volts.

Once fully charged the full charge can be maintained with a float charge at around 13.5 volts.

[SkinnyPete]

My 10 year old 981 is on its original battery which I find quite remarkable as 4-5 years ago it was throwing up low voltage messages.

Stop start hasn’t worked in six months though so I’d imagine it’ll be on its way out soon.

Also always charges at 15.2v since the day I’ve had it.

[981Boxess]

SkinnyPete said:

My 10 year old 981 is on its original battery which I find quite remarkable as 4-5 years ago it was throwing up low voltage messages.

Stop start hasn’t worked in six months though so I’d imagine it’ll be on its way out soon.

Also always charges at 15.2v since the day I’ve had it.

You have had your monies worth then, batteries are lasting a lot longer nowadays.

Apparently the stop start is the first thing the system shuts down when the battery is on its way out.

[ATM]

981Boxess said:

SkinnyPete said:

My 10 year old 981 is on its original battery which I find quite remarkable as 4-5 years ago it was throwing up low voltage messages.

Stop start hasn’t worked in six months though so I’d imagine it’ll be on its way out soon.

Also always charges at 15.2v since the day I’ve had it.

You have had your monies worth then, batteries are lasting a lot longer nowadays.

Apparently the stop start is the first thing the system shuts down when the battery is on its way out.

I've found if I give the battery a good charge with a real charger then the stop start will work fine. But that was a few years ago now. Not tried it recently.

[Armitage.Shanks]

The first thing I do when I get in is turn off the stop/start. Hideous device.

[ATM]

Just remembered...

A few years ago I read that we should connect the charger to positive on the battery but negative on the car.

Is anyone else doing that?

Something about helping the car understand its being charged. Could help explain the start stop working well after a full charge.

I've not done that recently because I find it easier now to swap out the battery and charge in the house.

[stanlow45]

ATM said:

Just remembered...

A few years ago I read that we should connect the charger to positive on the battery but negative on the car.

Is anyone else doing that?

Something about helping the car understand its being charged. Could help explain the start stop working well after a full charge.

I've not done that recently because I find it easier now to swap out the battery and charge in the house.

I think you mean the negative point is connected to the bodywork not the battery negative to prevent shorting when on charge. Here is a handy thread:

https://www.pistonheads.com/gassing/topic.asp?h=0&...

[981Boxess]

stanlow45 said:

ATM said:

Just remembered...

A few years ago I read that we should connect the charger to positive on the battery but negative on the car.

Is anyone else doing that?

Something about helping the car understand its being charged. Could help explain the start stop working well after a full charge.

I've not done that recently because I find it easier now to swap out the battery and charge in the house.

I think you mean the negative point is connected to the bodywork not the battery negative to prevent shorting when on charge.

It isn't about preventing shorting when on charge it has to do with charging 'the system' rather than just the battery in isolation. Back in the day when we fitted voltage drop sensing alarms you could not connect alarms direct to the battery as it masked small changes in voltage, same thing.

A lot of changes have had to be built into car charging systems to accomodate stop start/AGM battery technology, none of them good IMO.

[ATM]

981Boxess said:

stanlow45 said:

ATM said:

Just remembered...

A few years ago I read that we should connect the charger to positive on the battery but negative on the car.

Is anyone else doing that?

Something about helping the car understand its being charged. Could help explain the start stop working well after a full charge.

I've not done that recently because I find it easier now to swap out the battery and charge in the house.

I think you mean the negative point is connected to the bodywork not the battery negative to prevent shorting when on charge.

It isn't about preventing shorting when on charge it has to do with charging 'the system' rather than just the battery in isolation. Back in the day when we fitted voltage drop sensing alarms you could not connect alarms direct to the battery as it masked small changes in voltage, same thing.

A lot of changes have had to be built into car charging systems to accomodate stop start/AGM battery technology, none of them good IMO.

I think it's for emissions. My mate is an accountant and he says his e90 had the best cigarette lighter for charging his vape. When he upgraded to an f30 his vape would take longer to charge. I'm not sure I believe that myself.

I think his point is that modern cars don't run the electrics at as high volts as these older cars.

So if the car can make the alternator run softer or more gentle then it will create less drag and therefore improve emissions. But it will charge the battery less and therefore stop start will activate less. So not sure what's best from an eco perspective. I'd guess less drag when running will always win. Maybe if running along the motorway a gentle charger can give the battery enough juice to support stop start once you come to a stop. Otherwise it seems pointless keeping the battery only partially charged.

But yes that's what I was getting at about connecting the charger to the car rather than battery. If the car sees the charger then maybe it is happier to activate the start stop because it knows [or assumes it knows] how much charge the battery has.

I was reading some posts from people using LiFePo4 batteries on their 981 in USA. It seems some people had problems where the car would start to freak out and I think this was caused by the car charging at 15.2v which is too high for some of the internal circuits of some LiFePo4 and they shut off charging. Therefore the battery will effectively go flat all of a sudden and worst case could leave you stranded or best case could upset some of the cars sensors. I did have a steering support error pop up on my dash which I now think could have been caused by a poor battery.

So the 981 can charge at a range as high as 14.9 to 15.2v. I think I've seen 15 on mine but don't remember the decimal. Will keep an eye on it. I'm still trying to figure out a good way to mount a little LiFePo4 so it can't move around.