Your Economy mode is something you'll have to live with, as unlike earlier C5s the time before Economy Mode engages is controlled by the BSI from information it received from a little unit you have called the Battery Charge Status Unit attached to the negative battery terminal.
This little device monitors the charge in the battery, the temperature and can trigger the LIN to 'poll' the battery at certain intervals when the car is asleep to determine charge levels. All this info will determine how long you can operate equipment without the engine running.
The C5 and especially the X7 with Hydraulic suspension is very battery power hungry, with some systems actively monitoring the car even when it is shut down.
- It starts the suspension pump going when the car is unlocked;
- There is the alarm, the ultrasonic detection;
- The starting of the Electro Hydraulic Power Steering pump at ignition on;
- Plus in your case you have the RT4 telematics system, which has to write any data to the hard drive when the ignition is switched off;
- Plus the internal fan inside the RT4 also has to cool the unit down when the engine is stopped;
- Oh and of course there is the monitoring of whether the fuel flap is opened for fuelling to determine if fuel has been added to the tank for the purposes of calculating the additive dosing, with the engine ECU also staying active to memorise the fuel level in the tank before stopping and after fuelling;
- The TPMS (Tyre Pressure Monitoring System) also 'polls' the sensors to determine the pressures and temperatures periodically to determine pressures;
- Plus the various ECUs that power down when they've finished sending their data to the other systems;
- You might hear a whirring noise from the engine periodically when switching the engine off - that is the EGR electrovalve testing itself / returning the butterfly control to 'closed' at rest.
These are just a few things to highlight what the X7 does without the engine running, so it is imperative to have a good battery in good order. I change mine whenever I get acquire a C5 so I know it is new. But I certainly would change mine no later than every 5 years - depending on usage. A poor battery will almost certainly contribute to electrical glitches when it's in a weakened state.
A tip also for you - if you ever charge the battery, it is recommended that it is charged on the vehicle - but make sure that you attach the negative charging lead BEFORE the Battery Charge Status Unit, not directly onto the negative terminal. This is so the unit knows it is being charged and can factor that into any data it sends the BSI.
Here;s a few pics of this magic unit:
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| Always attach the battery charger negative clamp to 'a' on the Battery Charge Status Unit when charging. | Here it is on the Battery. (and that's copper grease by the way not rust  ) |
