Electronics spins, water break under the starter battery

Hello together 🙂 I’ve been having several problems with my VW Phaeton 3.0 TDI Year of construction 2013 I’m going to spin a key, then the engine doesn’t start right away. So I’m turning keys again then it starts but the start process is like delayed. The button on the selector lever is blocked for 10 seconds longer than normal. The parking sensors go to red. And the front assist is simply switched off (without error) although by default. Then it happens in some cases. I turn it off and it’s back on again. Park sensors then go back on their own after a few minutes and the front assist can be activated as normal. So far so good. In winter I changed the comfort battery because the heater at – temperatures no longer wanted to. I changed the starter battery at the same time and found that everything was wet in the box on the right. Nothing thought about it… yesterday and the day before yesterday the mistake was again very often there again. Then I looked in there again and see again everything wet. My questions, do you have an idea where the water could come from? From above it does not seem to come then it runs behind the ECU / through the ECU. Can you tell me what this ECU is? Did you have maybe already similar problems? Thank you and nice Sunday 🙂