Hi All,

I have a 2002 Laguna 1.9 DCI that has a battery discharge problem. Below are the diagnostics I have performed so far.

8-month-old battery, drop test OK
Charging system tested OK

The car is driven 100 miles daily and starts the next day. However, when left for 2 or 3 days the battery is discharged. I am not leaving any electrical item on and there are no third party devices. I have checked interior lights etc.

I have checked the current drain by connecting a digital multi meter in series with the negative terminal. This test appeared OK with a 30 mA reading after about 30 seconds.

I suspected an internal fault on the battery even though it is new and tested. To eliminate it, I took it out of the car and left for 2 or 3 days. It's reading after this period of disconnection was 12.48V - OK.

There appears to be an intermittent problem with an electrical device "waking up" and not shutting down. Could anyone give advice on how to diagnose/solve the problem?

Any help greatly appreciated as I cannot afford to trade the vehicle.

Kind regards

 

If it's an intermittent problem, that can be tough to find.

Can you put a disconnect switch or relay on the battery wire to the electrical system (the smaller wire that is typically connected to the battery to provide power to everything but the starter motor)?
A relay could be controlled by a hidden switch under the dash to provide extra theft protection.

You could configure the relay to operate in the latching mode, so a push-button would latch it when the ignition is on, but would open when the ignition is turned off, so you wouldn't have to remember to turn it off (below).
The procedure would be to turn on the ignition, and then press the PB to apply system electrical power and latch the relay.

 

The battery kill switch is great but in this day and age with alarms and power locks not as convenient and also treating the symptom and not the root cause.

With your car off put a multimeter in current mode and inline with the battery. Take your parasitic drain reading... after that you will remove fuses one out at a time and look for a drop. Take note of the circuit. Then you will have to find what's on that circuit in a wiring diagram for the vehicle. It could be a bad relay (stuck), wiring issue or a number of other things. Electrical issues take a lot of time to diagnose in cars. Some power drain is normal. Typical battery has about 40-60 Ah. You are looking for something in the 500mA drain or higher.

I had a car with a ruined transmission because of bad wiring which got burnt insulation from being too close to the exhaust manifold, i changed all the sensors and solenoids in it... it would intermittently kick in and out of gear which is unnerving at 70 mph , it eventually ruined the clutches. The wiring for the trans was in that bunch. Now finding out the exhaust got too hot ( catalytic converter is right off it) because the CID was malfunctioning which is flooding the cat with unburnt fuel. I would put in a new wiring harness for the engine but can't be done without dropping the engine... so it has liquid tape and electrical tape keeping the wires apart.

 

Maximum current draw should be 30-50mA. Installing a kill switch does not fix the problem and that problem could get worse. Installing an ammeter in series is invasive and may disconnect and reset the fault. The best way to find acurrent draw is to use an inductive ammeter and wrap it around one of the battery connections. You will need to get it around all wiring going to the battery post. Clip on, let it go to sleep and measure. Do it each time until you catch the draw. If you have a remote starter or aftermarket device, disconnect it and you may find your problem gone. Good luck

 

One method for tracking a mystery draw on a battery is to remove one or more fuses when the car is switched off, and see which fuse stops the power draw. When you learn which circuit is the source of the draw, leave that fuse disconnected and see if the battery discharge over time stops. If it does, then you know which circuit to investigate, if not, you will need to experiment with disconnecting other fuses.

 

Somehow my post vanished, so here it is again.
A simple way to track the mystery power draw is to remove fuses while you ate monitoring the battery current. When you remove a fuse that stops the current, leave that fuse disconnected and see if the battery still runs down. If it no longer runs down then you know which circuit to investigate, but if it still runs down then you will need to continue removing fuses until you locate the circuit that has the mystery power draw.
On my one car it was a trunk light that did not always switch off, and would switch on when a door was closed quickly.
Your problem may be different, but that is the sort of thing that will cause problems. But pulling fuses is simple and effective and not likely to damage anything, so it is a worthwhile search method.