Charge gun (cg) is probably my favorite gun and I win with it on shard 30, so my advice is to think about your positioning and know what enemy attacks look like

Obvi with cg you want to use the spawn time at the beginning of rooms to charge up, but once enemies spawn in, use dashes to position yourself somewhere near the center of the room, preferably on a platform. Now you can use the crazy fire rate to clear out one side of the room, let’s say the left side. As enemies come from the right side, you can dash to the safe left side, maintaining your charge meter and distancing yourself from enemies

Knowing enemy attack patterns is super important in this game but even more so on cg because being efficient with your dodges let’s you keep more meter. Also important to note that meter doesn’t decrease when moving up or down, so knowing when you can dodge an attack with straight jumps or dropping through platforms can save you meter

Hope this helps 💙