Low battery korg x5

SOURCE: I dont know how to replace the internal battery on a Korg M1

You should be able to remove the top cover off your keyboard and see the quarter-size battery mounted in a holder on one of the circuit boards.
I don't recall the exact location on this particular model, but once you've located it, all you have to do is slide it out from under the contact spring that holds it in place and slide a new one in.
You'll want to make the swap fairly quickly as some models can lose their memory settings if battery power is lost for a relatively short amount of time.