Jeep Compass 2019 won’t start properly + Start/Stop disabled for years – battery problem?

My Jeep Compass 2019 1.6 Multijet started showing a message about 3–4 years ago saying that the start/stop system was disabled. About a year after that, we went on a long road trip across Europe, and interestingly, the start/stop system started working again—but only for two days before it stopped once more.

Around five months ago, the battery completely died. The car had been parked for a long time, so it discharged. We jump-started it using another car, and fortunately, it started. After that, we drove it for about 30 minutes on the highway at around 120 km/h to recharge the battery. During the drive, the voltage reached about 14.5V, which seems normal while charging. However, when the car is idle, the battery usually sits between 12V and 13V, most commonly around 12.3V.

Today, we had planned a trip to another country, but the car didn’t want to start—the battery seemed dead again. After several attempts, it finally started.

I’d also like to point out that the start/stop system hasn’t worked for a long time now. From what I understand, this system is very sensitive to battery condition, so I’m wondering if the issue could be related to a weak or failing main battery, or possibly the auxiliary battery (if equipped). It could also be something simpler like dirty or corroded terminals, or in the worst case, damaged or burnt wiring.

I’d like to know if anyone else has experienced similar problems with batteries, auxiliary batteries, or electrical connections in this model, and what the most likely cause could be