Déclic literally means 'click' (like a switch) or 'trigger'. However, it's often used metaphorically to mean a 'turning point' or a sudden realization.
In the song, the lyrics "On cherche le bonheur / On attend le déclic" (We're looking for happiness / We're waiting for the turning point) perfectly capture the feeling of anticipation for that moment when everything falls into place or a new understanding dawns. It's a common yet profound expression in French.
CARLA sings about a generation running on empty. The chorus names it plainly: Batterie faible (low battery), On est de ceux qui attendent l'étincelle (we're among those who wait for the spark), Mais y a personne pour répondre à l'appel (but there's nobody to answer the call).
The verses fill in the days: laughing on the boulevards, praying comme s'il n'était jamais trop tard (as if it were never too late), then going back to ces écrans qui obsèdent (these screens that obsess). Under it all, au fond de nos cœurs électriques (deep down in our electric hearts), they keep looking for happiness and waiting for le déclic (the click) that would switch them back on.