2016 ds4 wont start

Hi, new member here, wifes 2016 ds4 will not start. Issue started a week ago with tyre pressure warning along with handbrake warning and battery warning, checked trye pressures and made sure all the same, tyre warning went away. Still had battery and hand brake warnings. Checked battery with multi meter readings were 12.6 volts sitting and 14.7 when running. Wife has had to re-insert key several times before car would start, once running there were no lights ir warnings, this weekend however we tried to start the car several times and the key does nothing, turns on the ignition and throws up a battery warning but trying for several hours and m turning the key the car will not start, anyone got any ideas, there is power as central locking works, mirrors work, lights work just will not turn over

Can anyone shed any light on where to look?
Many thanks in advance.

Edited this post…
found this on youtube https://www.youtube.com/watch?v=IuUlTfdBXbY

followed the directions and have got the car running, however when turned off will not start again unless the fuses are bridged as in the clip, while running still having battery charge warning and checked the voltage while running and now down to 11.93 v.
anyone changed their own alternator on one of these and any issues while doing so?