Peugeot 408 battery sensor issue

Sounds like a defective battery sensor. The sensor monitors the battery's voltage and overall health. When it fails, it can cause those exact symptoms – weak starts and flickering lights. Have you checked the voltage with a multimeter? A healthy battery should read around 12.6 volts when the engine is off.

A multimeter, eh? I've heard of those... but I'm not exactly an electrical engineer. Where exactly do I stick the probes to check the voltage? And what am I looking for besides 12.6V? Like, how low is TOO low?

Okay, using a multimeter can be tricky if you're not familiar with it. Basically, the black probe goes to the negative terminal of your battery, and the red probe goes to the positive terminal. If it's significantly below 12.6V (say, below 12.2V), especially after the car's been sitting for a while, it's a strong indicator that the sensor is faulty or the battery itself is failing. Honestly, with those symptoms and mileage, best to take it to a trusted mechanic to diagnose it properly. Could save you a headache!

Thanks a bunch! I was dreading messing around with it myself, especially after you explained the multimeter thing, haha. Took it to my local garage, and you nailed it – the battery sensor was shot. Cost me 315€ to get it replaced, but at least the disco lights are gone and the car starts like a champ again!