hello. after reading many posts on the internet, now I have the following information : x-type has a smart charging battery control driven by ECM.
the problem is : at start-up, the battery charge is rising from 12.5 V to 13.9-14.1v. no battery light warning. after 8 to 15 minutes, suddenly charge drops to 12.6-12.9 V, no matter if the RPM is high or idle. starting all lights and dash fan to max, voltage drops to about 12.1V, but no warning light. sometimes, the battery warning light turns on and never goes off till I restart the engine. sometimes the battery light is on after 20-30 seconds after the engine starts, even the battery charge is at 14.2V. even the measured charge is at 14.1-14.2, with all electric consumers on, charge drops till minimum 12.5v. tested on other two cars, but charge remains about 14.1V with a second drop to 13.9 when starting a large consumer ( older BMW and newer Renault).the previous battery died on this car after 4 months. replaced ( not by me) charging relay, new battery, but after two days the problem is still here. searching on the internet for answers, come to my attention the fact that if you put out the wire from pin number 3 on generator, this will act like a regular generator, no smart charge. is it possibile? worth a try? what about irregular charge :ECM bad? wiring from generator to battery? it's very difficult to work on the generator,due lack of space...

 

The battery cables are known to cause weird issues when they go bad, if it were my car i would change the cables before trying to band aid the symptom. There are some great techs here who will probably try and pinpoint the answer, but new cables are pretty cheap and a good investment on an older car anyway