Blue Smart IP65 Charger Operations Assistance

I’m trying to understand if my Blue Smart IP65 Charger 12/15 is working properly. I’ve read the manual and still not understanding so i’m hoping someone can explain. I have the Blue Smart IP65 Charger installed in my Campervan along with a Projecta Intelli-Charge DC/DC Lithium Charger to manage the charging and use of my 120 Lithium battery. When i drive the van, the battery fully charges up to 100% and about 13.5v even when small fridge is running. If I stop at a campground and plug into the mains power, and keep the fridge running, use some lights etc, I imagined the power would stay at approximately 100% / 13.5v. But at the moment, even when connected to mains power, the readings go progressively down over a couple of days, at the moment 78.6% 13.1v. The lights on the Blue Smart Charger show solid blue on L-ion mode and solid green on Storage. The Projecta Intelli-Charge DC/DC Lithium Charger shows flashing blue on Lithium mode. Is this the way it is supposed to work when connected to mains power, ie the battery gradually going down, or should it be always keeping the battery charged when connected to mains power? If it is supposed to use the battery for some time, will it get to a low point of battery % and v whereby the mains power kicks in automatically to run the fridge and lights plus recharge the lithium battery, if so at what point would i expect the maind power operation and charging to kick in? If someone could please explain I would greatly appreciate as electrics is not my strong point at all.

A 15a charger is not a suitable power supply for a portable fridge.

13.5v is not “full” for a Lithium battery, should be at least 14.2.

The storage voltage is 13.5V so either you are using more than 15A so it is not keeping up or you have a poor connection so the charge current is limited. Have you got the Victron Connect app so you can read the charger by Bluetooth, this should tell you what current is being supplied. See Sections 5 & 6 in the manual.