Meaning of icon next to current percentage charge

When I’m driving using ABRP it shows its idea of the current percentage charge of my vehicle. I believe it gets this information by communicating with Citroën’s servers. Next to this figure there is an icon like the signal strength icon on a mobile phone. Sometimes it is red; sometimes it is green. Sometimes the bars are solid, sometimes hollow. What is this icon trying to express? I can’t find it documented anywhere.