Megane weak battery starts

I had a similar problem with my Megane (although it's an older model). The weak starts and flickering lights sound very familiar. Have you checked the voltage sensor on the battery itself? It could be faulty and giving incorrect readings, leading to these symptoms. I would recommend getting the battery properly tested at a workshop.

Thanks for the quick reply! Where exactly is this voltage sensor located, and is there a way to test it myself before heading to a mechanic?

The sensor is usually attached directly to the negative terminal of the battery, or very close to it. Visually inspect the wiring for any damage. Testing it yourself would require some specialized equipment to read the signal it's sending to the car's computer, to see if it's within spec. I would just take it to a workshop. I had to replace mine last year, and it was a relatively quick job to diagnose and fix, and the symptoms went away immediately. Definitely worth checking out, since a defective sensor can eventually cause problems with the entire charging system.

Thanks, that's really helpful! I'll take it to a workshop to get the battery sensor checked. They replaced it and the issue is now resolved. The defective sensor caused the battery not to charge properly. Repair was 315€. I really appreciate the advice!