Fluence key fob battery issue

Indeed. The symptoms you've described: failing keyless access, error memory storage, and intermittent locking/unlocking functionality strongly suggest a depleted key fob battery. Have you attempted any preliminary diagnostic procedures, such as measuring the open-circuit voltage of the battery within the key fob?

Measuring the voltage? No, I haven't gone that far. I figured it was a simple fix. What voltage should I be looking for, and what kind of battery does the Fluence key use?

The typical nominal voltage for such batteries is 3V. A significant deviation below this value, say 2.7V or lower, would indicate significant depletion. The Renault Fluence typically utilizes a CR2032 type battery. While it is understandable that you expect a simple fix, neglecting proper diagnostics can sometimes lead to misdiagnosis. If you are not comfortable with electrical measurements, consider consulting a qualified technician.

Okay, thanks for the info. CR2032, got it! I'll grab a new one and give it a shot. If that doesn't work, looks like I'm off to the shop. New battery (cost me 37€) and everything is working as expected again!