Major electrical issues

[Ds5 airdream]

I was driving my ds5 automatic when it went into limp mode with it showing major electrical fault repair and i had to use the gears in manual using the padels and the sat nav was not working but once I got home it was completely dead nothing would work and lights were flashing on and off on there own plus the central locking also packed up and the dash engine light stayed on permanently? Any advice from anyone please

[xantia_v6]

The first thing to check is the battery voltage.

[Ds5 airdream]

Hi the battery I had in was totally ruined after a week because what ever the problem is it drained it completely and I bought a brand new battery yesterday but the fault is still there, nothing