Auxiliary battery in trunk

[angusc]

Hi,

I just replaced the main battery under the seat and while looking through the hand book found pictures of a battery in the trunk. When u removed the Bose unit there it was. I will replace it anyway as it is from 2006 so probably the original unit. But can anyone let me know the functionality of the two batteries, is there any user interaction required to switch from one to the other, which is the "main" battery?

Thank you in advance.

Sent from my SM-G935F using Tapatalk

[Loren]

All Cayenne models can optionally be equipped with a backup battery (starter battery). This backup battery ensures that the vehicle can still be started even if the vehicle battery (main battery) is discharged.

 

The main battery is the one under the driver's seat (LHD).

[angusc]

I replaced the auxiliary battery in the truck, but was thinking more about what you said regarding the main battery. I left my car parked for several months with only a solar trickle charger connected to the rear trunk cigarette socket. The battery died in August, as reported by my vehicle tracking device. I attended the vehicle in October and had to jump start with a remote jump start device. I drove the car for 2 hours and when I switched off it wouldn't start.

I had the main battery changed under the seat and the car started every time after that. Then I discovered that I had the auxiliary battery fitted and changed it. When i tested the old auxiliary battery it had 12.6 volts charge and then when I connected my battery conditioning charger it showed fully charged. Which actually indicated to me that the AUX battery is still ok.

So my query is that the vehicle should have started before I replaced the main battery but it didn't (because the auxiliary battery is good). That leads me to think the starter battery is the one under the seat....... I also read the Porsche auxiliary manual that talked about the auxiliary battery and that electrical load is from this one....But why wouldn't this be the case for my situation....?

I can't see anything within PIWIS about the auxiliary battery setup. How can I check the charging logic is working as it should? Also why would the rear AUX battery be used for starting when the starter motor is at the furthest point and longest cable run from it?

Finally I still get the time out message to save battery when parked and listening to the PCM.....I would have thought the time out would be longer for an AUX battery setup vehicle.

Sent from my SM-G935F using Tapatalk

[bancu]

In my experience...You need to turn your key all the way to the left to get the secondary battery into the picture after the main one is dead. This has always allowed me to start the vehicle.

[angusc]

Update:
Well I got another low battery warning from my tracker after 3.5 months parked up overseas. I went to collect the car and had to use my jump starter pack.

I checked the Porsche charging wiring diagram and see the starter batter is the one in the trunk.
I would really like to better understand the principal of the two batteries and why after long periods the low battery and can't start without jumper........

I have ordered a 50w solar panel, battery conditioner controller and remote display as I'm planning to install this to trickle charge both batteries and then can forget my flat battery issues (hopefully).

But I still don't understand how the car won't start even if the main battery is depleted by my tracker system and general electrical discharge.

Does the system switch from the main battery to the starter battery once the main battery is flat and that's why I end up not being able to start the car?



Sent from my SM-G935F using Tapatalk

[Loren]

From the 2004 Cayenne Technik Book...

 

"Battery
Depending on specification and air-conditioning zones, the Cayenne is fitted with a battery having a capacity of 340 A/70 Ah to 450 A/95 Ah. As on the Cayenne S and Cayenne Turbo, the alternator is water-cooled and has a nominal output of 2100/2660 watts, depending on battery capacity. All Cayenne models can optionally be equipped with a backup battery (starter battery). This backup battery ensures that the vehicle can still be started even if the vehicle battery (main battery) is discharged. The capacity of the backup  battery is 480 A/85 Ah.

If two batteries are fitted to the vehicle (main battery and backup battery), these are connected or disconnected to the bus bar in the power distributor through a relay. The switching of the two batteries is controlled independent of the load management (function is integrated in the vehicle electrical system control unit). The starter relay of the 2nd battery is actuated parallel to the starter relay. That means for every start the starter is supplied from both batteries. The backup battery is disconnected from the vehicle electrical system when the engine is switched off and then supplies just one consumer, the vehicle electrical system control unit.

 

For crash protection purposes, the backup battery is designed using fleece technology.

 

Note: The backup battery is accommodated in the spare wheel recess in the trunk. This installation location is also designated for the optionally available collapsible spare wheel and the subwoofer of the BOSE® High End surround sound system. This results in a restricted storage capacity in the spare wheel recess. On the Cayenne, the optional backup battery cannot be fitted in conjunction with a 17" collapsible spare wheel.

In order not to exceed the maximum permitted rear axle load, no Cayenne model can simultaneously be equipped with the backup battery, a full-size spare wheel on the external holder and a trailer towing device.

 

Vehicle electrical system control unit
On vehicles with two batteries (vehicle electrical system and starter battery), the electronics of the vehicle electrical system control unit are supplied by both batteries. The vehicle electrical system control unit evaluates the exact vehicle electrical system situation by comparing the sensed voltage with the permissible minimum voltage. On vehicles with two batteries, the load management always takes the voltage of the vehicle battery as reference. If the vehicle electrical system control unit detects a critical battery condition,
the consumption is reduced. For this the CAN bus requests some of the high voltage comfort consumers to reduce or switch off their power demand. By reducing the comfort functions with the “engine running”, the battery can be charged more. With the “engine off”, discharging of the battery can be reduced through the load management.

Currently the following consumers are integrated in the load management:
• Heated rear window, heated outside mirrors
• Heated seats, front and rear
• Heated steering wheel
• Heater blower (3-stage)
• Interior light, reading lamps, footwell lighting
• 12 V sockets

 

The following functions are activated by the vehicle electronic system control unit:
• Load management
• Side marker lights
• Low beam
• Cornering light, left and right
• High beam
• Auxiliary high beam
• Direction indicator light
• Headlamp leveling control
• Potentiometer convenience lighting terminal 31
• Terminal 58 d
• Interior and footwell lights
• Fanfare horns
• Dual washing pump
• 12 V sockets
• Electric fuel-pump relay 1
• Load relay
• Rain sensor
• Enable signal, heated seats"

[angusc]

Thanx Loren!

Can you help with some further information regarding the rear power sockets. Are they connected to the main battery or the starter battery (in wheel well)? The reason I ask is that my solar charger controller can maintain two batteries independently. So I need to have a connection to the main battery (under driver's seat) and a separate connection to the starter battery in the trunk. As I'm going to mount and wire the controller in the trunk it will be easy to run a dedicated cable to the starter battery. I'm hoping that the 12v power socket in the trunk can give me the access to the main battery to reduce running another cable through to the driver's seat area....what do you think?

Sent from my SM-G935F using Tapatalk

[Loren]

30 minutes ago, angusc said:

Thanx Loren!

Can you help with some further information regarding the rear power sockets. Are they connected to the main battery or the starter battery (in wheel well)? The reason I ask is that my solar charger controller can maintain two batteries independently. So I need to have a connection to the main battery (under driver's seat) and a separate connection to the starter battery in the trunk. As I'm going to mount and wire the controller in the trunk it will be easy to run a dedicated cable to the starter battery. I'm hoping that the 12v power socket in the trunk can give me the access to the main battery to reduce running another cable through to the driver's seat area....what do you think?

Sent from my SM-G935F using Tapatalk
 

 

I will have a look at the wiring diagrams if you give me the exact model and year of your car.

 

[angusc]

Thanx Loren, my car is Cayenne turbo S. 2006 it is a European left hand drive from Germany.

 

I note at the bottom of the charging system description that you kindly provided above, that it states the 12v sockets are controlled be the vehicle electronic control unit..... So I'm not sure if it is permissible to reverse charge through those sockets as the solar charge would have to pass through the controller as well.....

 

If you have the wiring diagram for the sockets it would be most appreciated if you could check/share with me.

 

Thank you once again.

 

Sent from my SM-G935F using Tapatalk

 

 

 

 

[bigbuzuki]

If your car has KESSY and a flat main battery, using the plastic dummy key will not start the vehicle.

 

You must remove the plastic dummy key and use the fob with the metal key to start the car.

 

With the metal key inserted the system will use the rear battery for starter operation.

[angusc]

Thanx for that tip, however I do not have the plastic key and always use the fob and metal key

 

Sent from my SM-G935F using Tapatalk

 

 

 

 

[angusc]

 
I will have a look at the wiring diagrams if you give me the exact model and year of your car.
 

Hi again Loren, Did you have any time to look at the wiring diagram for me? Thank you if you can.

Best regards Chris.

[Loren]

The starter battery is only used for starting - controlled by a relay when try to start.

Everything else is on the main battery circuit.

[angusc]

If your car has KESSY and a flat main battery, using the plastic dummy key will not start the vehicle.
 
You must remove the plastic dummy key and use the fob with the metal key to start the car.
 
With the metal key inserted the system will use the rear battery for starter operation.

Hi bigbazuki, just reading your reply again, so are you saying that if using the plastic key the car will start using the under driver seat battery. But using the metal key it would use the starter battery situated in the trunk?

Sent from my SM-G935F using Tapatalk

[angusc]

I hadn't trouble shot this problem yet, but I did make a modification to the system by installing a dual battery solar charger! Using a 60w solar panel. The system has a display that now showed both battery voltages, which help to identify possible other issues. As the battery under driver's seat never seems to charge above 12.6v and the rear trunk battery at 13.2v. When the engine is running the voltages of both show 13.8v
I'm leaning towards the battery change over relay or fuses issue and possibly something that is making a heavy demand on battery power when the car is parked........

Sent from my SM-G935F using Tapatalk

[bigbuzuki]

On 18/06/2017 at 9:42 PM, angusc said:

 

Hi bigbazuki, just reading your reply again, so are you saying that if using the plastic key the car will start using the under driver seat battery. But using the metal key it would use the starter battery situated in the trunk?

Sent from my SM-G935F using Tapatalk
 

 

Yes.

[angusc]

Thanx for the confirmation, would you have the test procedure for the battery change over relay or anything else for cars fitted with the additional battery? Thanx if you can help.

[ManMN]

My car is 2004 S.  The batteries (2) were replaced in 2013 by Porsche dealer.  I am now experiencing weird electronic problems .  As I recalled it from the past, weak battery contributes to weird  electronic problems, plus, the batteries are 5 years old, Its safe to planning replacing the battery(2)!  And here's my thinking, can I replace and use only 1 battery with a higher capacity rating? or am I stuck with 2 batteries? can I swap front and back battery?  I don't think my model year has any kind of battery registration feature like many later BMW cars does it? Any advice is greatly appreciated.  Many thanks.

[bigbuzuki]

Replace the the front battery initially as its 5 years of age.

 

There is no battery registration feature on your Cayenne.

 

Front and rear batteries are different capacities with the larger capacity in the front position.

 

Do not swap battery positions.

 

If your car is optioned with KESSY and you use the plastic dummy key to start the car, the front battery is used for cranking.

 

If you don’t use the plastic dummy key, the cranking operation is via the rear battery.

Edited July 14, 2018 by bigbuzuki

[angusc]

Hi bigbazuki,

 

I don't have a dummy plastic key, but I do have a metal dummy key that I had cut locally. So that key does not have the security chip. Would that key act and work like the Porsche plastic dummy key?

 

I have dual batteries and the KESSY systems installed. Also do you have any test procedure for the dual battery system and change over relay etc?

 

Thanx.

[bigbuzuki]

In your case with the metal dummy key substitute, ops would be the same as if your using the Porsche remote security metal key, the cranking power coming from the rear battery.

 

You need a plastic dummy key to have crank power from the front battery.

 

I am assuming that the sensing of metal versus plastic inserted into the ignition slot is how the system differentiates between the keys and which battery crank source to use.

 

Have you checked the electrolyte levels and measured the specific gravity of the cell batteries?

 

 

Edited July 14, 2018 by bigbuzuki

[angusc]

I actually replaced both batteries last year, my problem is that I leave this car parked for weeks on end and usually get the low battery message from tube tracker system around 7-8 weeks.

 

At the same time I did install a 100w solar panel and charge controller that goes to both front and rear batteries, but as I'm parked in a connected car park the panel can only get limited sunlight. (I prop the solar panel up in the front window and park facing south). This increases the time to a flat battery by another 4 weeks in summer time.

 

After normal driving I see that the battery voltages measure 12.2 volt on the front battery and 12.4 volt on the rear battery. Is this normal 'fully charged ' status from the engine alternator?

 

I have contemplated trying to install a master battery 'kill switch' so that all power would be disconnected as a last attempt to have full battery when I return to the vehicle, but I'm not sure where in the system such a switch would be installed.....would under the drivers seat have a place to disconnect both batteries? As the auxiliary battery setup seems to be two isolated power systems, it would I have to fit two kill switches?

 

By 'kill switch' I mean the single pole battery isolators that they use in some motor sports.

 

Sent from my SM-G935F using Tapatalk

 

 

 

 

[smithh]

As it happens I've fitted a Motor sports kill switch to my cayenne.  Mine is a 2008 GTS, and has the 17" spare and bose subwoofer. However, I needed a kill switch fitted.  So I've fitted mine to the base of the drivers seat.  I would figure on a car with dual batteries, there is no reason why you couldnt do the same.

Out of interest, I'm keen to take the bose out and fit a second battery under the wheel.  Not worked out details yet.

[angusc]

Well mine is a Turbo S with the Bose system but no spare wheel, so you could fit the auxiliary battery and keep the Bose if you wanted. I don't really see the benefit of auxiliary battery as it currently stands because it's still running flat after 4-5 weeks of inactivity. I will try the plastic key trick to see if it will still start off the aux battery at the end of this month as the main voltage is presently sitting at 10.42v so it ain't gonna start off that one.

 

Would you be able to provide any details on the kill switch and photo of how you fo haver it fitted? Any help to allow me to purchase one and the other parts required that I know will already fit would be great.

 

Thanx

 

 

 

[angusc]

On 7/14/2018 at 1:14 PM, bigbuzuki said:

In your case with the metal dummy key substitute, ops would be the same as if your using the Porsche remote security metal key, the cranking power coming from the rear battery.

 

You need a plastic dummy key to have crank power from the front battery.

 

I am assuming that the sensing of metal versus plastic inserted into the ignition slot is how the system differentiates between the keys and which battery crank source to use.

 

Have you checked the electrolyte levels and measured the specific gravity of the cell batteries?

 

 

Hi again,

 

I eventually ordered a service key (plastic) with no electronics and headed to where my Cayenne was parked with flat battery. I tried to start the car with the service key but it did not work and the key was held in the ignition lock due to no power.

 

So it didn't seem to switch over batteries for cranking......unless both the rear and front battery were both discharged.

 

After jump starting and later fully recharging the car on a trickle charger, I tried the service key again. But I only see a message about the immobilizer  being active on the dash display and the key can't crank the engine. Is there something else that I would need to do to get the car to crank from the front (under drivers seat) battery?

 

Thanx for any support.

Edited November 23, 2018 by angusc