Battery charge fault
2016 Citroen C4 1.2

Usually caused by faulty alternator , needs charging rate checked with a meter .

I have this problem with my 2015 c4 was told battery was scrap..replaced it with new battery, expensive, worked ok for a few weeks..light and warning came back on...alternator checked twice, charging fine, told to charge battery on home charger...light went out for about 2 days then came back on.
Won't go off at all now. Auto sparks are baffled by this and so am I.

Important you LOAD test alternator . Depends on make and type of alternator , lot of cheap recon units which are often not very good and a waste of money . Also wiring needs checking

There's a module that sits in front of the battery. That is what causes the issue. It also flattens the battery if left for long time. Citreon quoted me £450 to replace.

It could be as described above. There is a Battery Protection Unit that sits on top of the battery Part code is 9665878080 and it is manufactured by Valeo. It has some fuses on top and hanging down from it in front of the battery is a relay controlled by the electronics underneath it. I am now on my 3rd one. What I think happens is that the relay coils protection circuit is destroyed by the back emf from the coil and then the relay does not switch over which discharges the battery. The actual relay is fine or at least it was on the one I cut open. Diagnostics should throw up the fault code for a non working relay on it.