Ok... so I checked again individually each batteries when the wave was 0% with « charge battery » message. Every battery was at around 6.30v and the weaker one was 4.85v

So... battery issue and replacing all 4 batteries should fix that?

Also, I find it quite weird that I was now at 43% and in an instant just by power off and power on again it dropped to 0%, without even starting to drop and losing some percentage every few minutes. Its like if I stay on it goes down to 0% fast but gradually but the moment I shut it down and restart now its already 0%