Battery Conundrum

[Steve Brookes]

When I got my 987 a few weeks ago it still had the original battery fitted. Being 5 years old it's clearly on its last legs. Very laboured turnover when starting the car.

So I put in a Bosch Silver S5 which in my experience is a much better battery than the Porsche Moll version. The car now turns over properly on starting. However, I noticed that the interior light and footwell lights stayed on even though the doors were shut and the engine on (switch in the courtesy position). So I have to have the interior light in the off position all the time. If I put the original battery in the lights work as they should with the switch in the courtesy position!

How the heck does that work? Can the car tell when its got a non-Porsche battery? Do I have to buy a new Porsche Moll battery to get everything to work normally?

 

[whhuer]

A strange one. If it is of any help I replaced the five and a half year old original battery in my 2.7 a week ago with a Bosch S5. I assume the cars are of the same age. No problems encountered but had the expected ECU failure alarm which cleared after a quick run down the road. Could it be that something requires a re-set?

 

[Steve Brookes]

Yes I get the PSM failure warning when changing the battery but that clears as soon as I drive it (regardless of what battery is fitted). But the interior/footwell light issue stays while I have a non Porsche battery on. As soon as I put the old Porsche battery on the lights act normally. I've tried three non-Porsche batteries now and they all give the same effect.

 

[vitesse]

Doesn't seem a very scientific approach from a "scientist" does it?You know darned well that all a battery is is stored electricity & the electrons don't know Porsche from Adam[]So it can only be the "Lymn" effect-a confluence of dam resistance ohm from ohm![]

 

[Richard_Hamilton]

ORIGINAL: Steve Brookes

Yes I get the PSM failure warning when changing the battery but that clears as soon as I drive it (regardless of what battery is fitted). But the interior/footwell light issue stays while I have a non Porsche battery on. As soon as I put the old Porsche battery on the lights act normally. I've tried three non-Porsche batteries now and they all give the same effect.

Am I reading your initial post correctly, and the interior lights are on while you are driving the car, despite being switched to the courtesy position?

I suppose you could try partially flattening the Bosch S5 before fitting it, to simulate a Moll. [] Pehaps rig up an old headlight bulb, or something to load the disconnected battery, for an hour or so. Keep an eye on the voltage with a multimeter, until it goes down to about 12.5V. It does seem to be voltage related. I can't think that Porsche use manufacturer-specific volts and amps!

It seems quite bizarre, I have to say.

 

[Steve Brookes]

Thanks Richard. To clarify, yes, the interior/footwell lights stay on while driving when the Bosch S5 is fitted (but the door lights go out) and the switch is in the courtesy position. All lights act normally with the Porsche Moll fitted (but it struggles to crank the engine which is why I don't want to carry on using it).

The Porsche Moll which is out of the car at the moment reads 12.45 volts. The Bosch S5 which is in the car at the moment is currently reading 12.11 volts. The Moll is an 80 Ah battery, while the S5 is an 85 Ah battery. I've also tried both batteries that I have for the 964. These are 70 Ah batteries and both produce the same weird 'interior light staying on effect'.

As you say, it's all very bizarre! []

 

[Richard_Hamilton]

To make a comparison, you need to measure the open circuit voltage of the S5 battery (ie disconnected). Porsche say anything under 12.5 for a fully charged battery is a sign that the battery is on the way out.

Doesn't sound like it will solve your problem though. At first, I thought that perhaps it had slipped back into energy saving (transit) mode, as I have seen that happen to a few 986's, but it can't be that if the Moll battery doesn't do the same.

 

[whhuer]

A few thoughts which might or might not help (trying to dust off the grey cells or what little were left when I retired), could it be a problem tha thas been there for a while but not showing up with the Moll battery on its way out. The following may be worth checking if you havn't already.
Do the interior lights switch off normally when the doors are closed/locked
Do they switch off when the ignition is swiched on without starting the engine (i.e. battery at about 12.5v instead of about 14v when being charged by the engine.
Thats all I can think of, unfortunately I find modern car electrics/electronics a bit beyond me.

 

[Steve Brookes]

ORIGINAL: Richard Hamilton

To make a comparison, you need to measure the open circuit voltage of the S5 battery (ie disconnected). Porsche say anything under 12.5 for a fully charged battery is a sign that the battery is on the way out.

From memory the full charged S5 was 12.85 volts before I put it in. The smaller 70Ah battery that I tried yesterday and is now out of the car is 12.57 volts when I tested it on the bench a few minutes ago.

 

[Steve Brookes]

ORIGINAL: whhuer
Do the interior lights switch off normally when the doors are closed/locked

Yes, when the switch is left in the courtesy position all interior lights go out when the car is locked. This applies to all of the batteries.

ORIGINAL: whhuer
Do they switch off when the ignition is swiched on without starting the engine (i.e. battery at about 12.5v instead of about 14v when being charged by the engine.
Thats all I can think of, unfortunately I find modern car electrics/electronics a bit beyond me.

In that situation the interior/footwell lights go out with the Porsche moll but stay on with all the other batteries.

But I have a question for you...have you got an extra wire that goes to the earth terminal? On my previous 986 there was just a normal single earth strap but the 987S appears to have a tail wire aswell.

 

[Andy Fagan]

Why not try putting a booster pack to the battery leads when changing from the genuine battery to the replacement so that the power is not cut during the swap. Then see what happens.

 

[Steve Brookes]

ORIGINAL: Andy Fagan

Why not try putting a booster pack to the battery leads when changing from the genuine battery to the replacement so that the power is not cut during the swap. Then see what happens.

I don't see that will do anything Andy. I can swap between the moll and the S5 all day long. The simple fact is that when the moll is in, the lights work normally. If I then put he S5 in (or another battery) I get the lights problem. If I then put the moll back in everything is fine again (except of course that it struggles to turn over the engine which is why I don't want to use it).

 

[Andy Fagan]

yes but you are interupting the continuity of supply just swapping them.

 

[Steve Brookes]

Well if that's the case it looks like the only solution is to take it to an OPC and get them to fit a new battery. Anyone know what that would cost?

 

[vitesse]

Steve,Have you asked John or Danny about this -they might have some tips-.

 

[Steve Brookes]

ORIGINAL: VITESSE

Steve,Have you asked John or Danny about this -they might have some tips-.

Not yet but they've only got limited diagnostics for the 9x7 models so might also be scratching their heads on this one. The issue I'm seeing seems to suggest that somehow the Moll battery is coded to the car. While Whhuer has managed to put an S5 on his 2.7 with no problems, my guess is that something got changed on the 3.4 to prevent non-Porsche approved batteries being used. The interior lights staying on being a 'tell tale' that a non Porsche battery is fitted. I also guess that many 3.4s are still under extended warranty therefore if they have had a battery changed they will have a Moll fitted at an OPC. So, it looks like this conundrum is not going to be solved for sometime yet.

BTW apart from the nuisance of having the interior light switch in the off position, it's an absolutely cracking car. []

 

[Motorhead]

I symapathise with your plight Steve.

Just a thought but it sounds to me that, at this stage, it would be very useful to have a look at the wiring diagram if you can get access to one somewhere. It might give you a clue as to why you're experiencing such an odd phenomenon.

I really can't believe that Porsche would be so crass as to discourage the use of "after-market" batteries otherwise I would have thought that we'd have had simliar postings on the forum.

Good luck.!

Jeff

 

[vitesse]

I agree-it would need a chip processor with a signal generated by the battery-hence my sly comment about "science" -unless the Moll battery has something on it which contacts a receiver thingy when fitted to the car-one way to check would be to use jump leads with the battery outside the car-I still think all electrons are equal[8|]

 

[Steve Brookes]

Au contraire chaps....until someone comes along and says they've put a non-Moll battery in their 3.4S with no problems I'll believe there IS a conspiracy theory at work here. At least this thread is turning into a source of amusement for us all. []

I hadn't thought of secretly hidden in the battery but I've already transferred the bar code from the Moll on to the S5 to try and fool a hidden bar code reader under the scuttle that is spying on me. [] Maybe the next step is to pour the life acid out of the Moll and break it open in search of the Porsche bug inside and then wash down the lead and sell it to a pikey. []

Some day this conundrum will be cracked but in the mean time....I'll carry on driving with S5 fitted and the light switch clicked to 'off' as I've got more pressing expenditure coming up in the next month or so..like a couple of tyres! [8|]

P.s. Colin, I'll freely admit that as a biologist I'm much more comfortable with touch feely things rather those damn electrons that I can't see but have given me a bit of a shock once in a while. []

 

[whhuer]

There is an additional wire to the negative terminal, as per the photo which hopefully has uploaded.
My thinking is that as there are a number of items which control these lights, ie door switch, door locking, ignition and manual switch, with a delay if the car is not locked, then an electronic circuit will control the operation, possibly via a solid state relay. With a good fully charged battery the voltage with the engine running the battery voltage will be about 14v but if the battery is on its way out then the voltage will be lower. If one of the electronic components is sub-standard then this could cause the problem you are encountering. Hopefully any such electronic circuits will not be part of another module, i.e. the ECU.

Regards
Wolfgang