My battery suddenly has an X over it, out of nowhere

My battery icon suddenly got a black X and my mac won't detect the battery.

I find this quite odd since earlier today it worked perfect but as I returned from school and plugged my macbook in, the battery went off.

I have read numerous guides on how to reset the SMC ( Shutting down the computer and powering it on while holding down certain keys ). Only problem is, that it didn't work. I tried this multiple times but every time i pressed the power button afterwards it just turned on normally.

Has anyone encountered this problem, and/or is there an alternative way to reset the SMC / Or fix the battery without having to take it to the store/repair.

I have a lot of work to do meaning that I can't afford to wait 2-3 weeks before it gets returned if I have to take it to a store

Best Regards & thanks in advance