Hi guys,

I’ve recently been having issues with a flat battery. The car is 12 years old so first thing I did was replace the battery as I thought it was down to age of the old battery. However since putting a new one in it still has the same problem where the car won’t start after leaving it over the weekend. Has anyone experienced similar issues ? Could this be a faulty alternator?

Edited 28 October, 202528 Oct by Tom100312

Hello Tom, welcome to the forum.

Have you checked the battery terminal voltage while the engine is running?

Does your vehicle have Stop/Start? If so, was the new battery adapted (coded) into the vehicles BCM?

Thanks for the reply! Battery is pushing out 13.8V whilst idle and under load 13.5V. It doesn’t have stop start.

Thanks, that would seem to indicate the alternator is charging ok.

Next thing to check is that everything is actually switching off when the ignition is switched off - check interior and exterior lights including trunk light.

Is the infotainment system original, have any changes or additions been made recently?

From what I can see no lights or anything is left on. The infotainment system is the original. It had an aftermarket tow bar fitted however I pulled all that out as the relay box all corroded. I have attached photos to what I pulled out.

Hmm, defo not a specialist or dealer install!

Have these battery issues occurred since the wiring removal?

Yes it has carried on since removing the wiring. I’ve also pulled the fuses for the radio and left it over the weekend and it’s died on me. The battery drops to around 10.5V so it’s not a major draw. Got the battery tested and that was saying it’s in excellent condition.

That suggests that there's a parasitic drain somewhere - to identify what is causing it will require an ammeter in series with battery lead (or Amp-clamp meter) and disconnecting possible loads.

I don't know if your vehicle has can bus wiring.

Do you have heated mirrors, seats or rear window?

Until you get to the bottom of this, seriously consider disconnecting the battery while car is not in use - continued deep discharges are very bad for your new battery.

At 10.5 volts, battery is completely discharged.

Thanks for the advice. It’s booked into the garage on Thursday so hopefully they get to the bottom of it.