X7 flat battery

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X7 flat battery

Post by faddy »

Currently not driving for medical reasons and after two weeks of non-use discovered my X7's battery was completely dead (no remote unlocking or dashboard lights). Took it off to charge, open circuit voltage was 5.5v. After charging, with battery still off the car voltage has only dropped a fraction of a Volt over two weeks. I'd previously had no problems with the battery over the twelve months I've had the car.

Any thoughts as to why it discharged so quickly? Would an armed alarm have been sufficient?

Any BSI related things I need to do when reconnecting the battery? There was, obviously, nothing I could do before disconnecting it.
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Re: X7 flat battery

Post by wheeler »

Do you know how old the battery is? If its over 5 years old it may be coming to the end of its life.
Ideally you want to check the alternator is charging ok & check the current draw when the car is at rest to confirm there is nothing wrong there.
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Re: X7 flat battery

Post by Paul-R »

No real thoughts on the cause but it certainly shouldn't have discharged that quickly. I've left my X7 for 6 weeks when I've gone on holiday and it's started fine on my return.

I've noticed that in a two PSA vehicle household that operating the remote fob of one wakes up the BSI of the other so possibly if you're next door to a car park or something like that then it could, perhaps, keep waking up? One other thing that might bear looking at is if your car has wet suspension then the pump runs when you unlock the car. Excess use might have a bearing?
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Re: X7 flat battery

Post by GiveMeABreak »

The X7 battery can discharge quickly - the rate can depend on engine, kit and options too. Different number of ECUs to close down parameters to write, fans to finish cooling (as in head units on vehicles with Nav systems) etc. Another example is if you have the Tyre Pressure Monitoring System - this triggers periodically to check status, then there are the LEDs for the locking / alarm system constantly flashing every few seconds.

None of these should adversely affect the battery though - but if a battery is not in peak condition, or short trips are a regular feature thus not allowing a significant amount of time to charge the battery, night use or use of a lot of power-consuming equipment, added to a period on non-use as in your case can all take a toll on the battery.

This is a more comprehensive list of possible causes for a discharged battery:
  • Incorrect use by the customer :-D (don't ask)
  • Poor resistance of the battery terminals
  • Presence of power consuming equipment in operation
  • Presence of faults on the multiplexed passenger compartment CAN
  • Presence of faults on the remote controlled triggering line
  • Unwanted triggering of the multiplexed passenger compartment CANs
  • Unwanted triggering of the multiplexed LIN
  • Unwanted triggering of the built-in systems interface
  • Passenger compartment multiplexed CAN maintained at the triggered status
  • Multiplexed LIN maintained at the triggered status
  • Built-in systems interface maintained at the triggered status
  • Engine not starting
  • Presence of faults on the central power switch positive supply
  • Central power switch maintained at the triggered status
  • Power harnesses : Body earth, engine earth, positive electrical harness between the alternator (voltage transformer on hybrid vehicles) and the battery
  • Alternator faulty (Except hybrid vehicles)
  • Battery faulty
So do you have any third party equipment plugged / wired in like phone chargers or other kit? Worth unplugging these if you do when not in use.
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Re: X7 flat battery

Post by faddy »

Thanks for all that Marc. (Very) short journeys may certainly be an issue for me, though I've always tended to assume (naively?) that if a car starts without fail there can't be too much wrong with the battery or its state of charge.

Is there anything BSI related I need to do when re-fitting the battery, bearing in mind that it was flat as a pancake when I took it off?
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Re: X7 flat battery

Post by myglaren »

Whether this is still true I know not but I once read that to restore the charge taken by starting the car one must drive for at least fifteen minutes at a reasonable pace.
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Re: X7 flat battery

Post by GiveMeABreak »

Unfortunately, on short journeys, the alternator may not have enough time to completely recharge the battery and replace the energy discharged through standing still (where it still uses some current) and this can have a cumulative effect.

As the battery age increases, its ability to hold a full charge diminishes and this will ultimately affect starting performance.

As for battery disconnection and connection, follow the procedure here:

BSI Reset / Battery Disconnect / Reconnect Procedure
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Re: X7 flat battery

Post by admiral51 »

With modern vehicles post 2000 ish the battery does a lot of work, it only takes one cell to go awol and game over, yes you can jump start it and run it all day, following morning not enough amps to start.
Looking at OP cars it appears to be a 2008 C5 so given battery life of around 5 years if changed at those intervals then it would be due a change and the cold weather probably has not helped :)
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