Leisure batteries not charging

Hi, im not very electrical minded atm and my terminolgy maybe off. But i will be learning. So i brought my victron kit and paid to have it installed as i dont have the know how or the time to get to know how! All has been going well since the kit has been installed in my van, however. Last week i noticed my smart meter was not going up in charge even after a 2 and a half hour journey. The dc-dc charger was on. So i emailed Nohma, who i brought the kit off and so it started. This is where im up too, with emails and contact from Nohma and the company that installed the kit.

So i sent those over requested by Nohma, and i also told them that an electrician at work had tested the fuse board with a multimeter and all fuses are fine.

Then i got the reply : According to the screenshots, the input voltage from the alternator is very low. What voltage is your alternator putting out when measured at the starter battery?

The electricians i work with again kindly checked for me and i got : 11.9 volts when engine was idle. Key turned (but engine not running) 12v when key was fully turned they said the voltage again dropped.

Nohma replied : Are you saying that with your engine running, your starter battery voltage is remaining at 12V?

Depending on the vehicle type, it might help to turn on your lights and hold the engine revs at ~2000RPM. If you still have a voltage below 13V, then this would indicate that you have an issue with your alternator

to which i responded: That i didnt have the engine running but have ordered a multimeter and will do it this weekend.

Does anyone have any ideas so far i will be testing with the multimeter but just wanted to put it out there, thank you

So i went back to where i had the system installed, as they kindly said they would take a look. He checked the dc - dc charger which had no green ‘on’ light, and the voltage was not getting up past 12.8 volts i think it was ( according to the victron app) and then it would drop back down to 12v. Also the dc - dc charger was quite ‘warm’. He disconnected the charger and i said i would re charge the batteries through the 240v inverter , which should hopefully see me through the next week. He stated that i need to configure the battery monitor with the 2-100ah batteries i have. As i reset the battery monitor in the hope that this sorts the problem. ( i am a novice). So that should be 1 of todays jobs, searching and reading how to configure the battery monitor and the cuurent state of charge of the batteries. I also need to contact Nohma at some point and ask for a possible replacement, im sure the dc charger is stii under warrarnty. The fitter who installed my electrical system did show me a dc dc charger-the same as mine that ‘burnt’ out, you could still smell a slight burn from the unit itsself. Apologies on my terminolgy and descriptions of some things, this is new to me and i am learning, thank you