MacBook switches off, from any kind of hard processing work

I spilt plain black coffee onto my MacBook Air , a while ago, around August last year. I immediately took it apart and cleaned it with 99% rubbing alcohol. I made sure it was completely dry before I put it back together. It switches on, and works fine, doing simple tasks, such as YouTube, word, excel etc. Then as soon as I try to use blender, or play any kind of game, I even tested(Minecraft)and it couldn’t handle it, it either lags insanely badly, or completely switches off. It has to be plugged in to work, the cable light is constantly orange. I have done a diagnostics, and it says my battery may not be functioning correctly (but my friend said that MacBooks cables go green if a battery isn’t detected), so I don’t know what is wrong, and I would like to repair it as soon as possible. So if anyone could help me I would appreciate it so much( I would also like to say, that the battery percentage drops by a 1 every now and then, and does not go up)