Transit key battery low

That sounds familiar. I had a similar issue with my old Renault Megane a few years back. Keyless entry started acting up, and then the range got shorter and shorter. Eventually, it just stopped working altogether. Did you try the spare key to rule out other issues?

Spare key exhibits the same behavior. Did replacing the battery in your Renault key solve the problem?

Yeah, replacing the battery did the trick for my Megane. Though, I remember reading somewhere that some cars need to have the key reprogrammed after a battery change. I'm not sure if that's the case with your Transit, but maybe it's worth checking the manual or taking it to a workshop. They'll probably sort it out quickly.

Thanks. Battery replacement (CR2032) in key fob rectified the issue. Total cost: 37€.