I Have a Epiphone AJ200SCEVS electro-acoustic, which has a built in tuner in the electronic system (there's probably a more technical term for that but IDK it). Ideally when you click the button to turn the tuner on its supposed to stop the signal to the amp, however the tuner now stays on 24/7/365 unless you take the batteries out.

This is causing me two problems:

1. My ELECTRO acoustic, is no longer "electro", since the tuner wont let any signal get to the amp

2.since i can't turn the tuner off, it kills brand new batteries in a matter of hours.

does anybody have any ideas about what might be wrong with it and how difficult/costly it would be to fix?

Any help is always appreciated.
Don't go chasing polar bears in the great unknown... Some big, friendly, polar bear might wanna take you home.
These are solid-state units, and unfortunately I imagine it will just have to be replaced. Is it under warranty? If so, you're likely OK. If not.... Parts and labor might be almost as much as you paid for the guitar....
Either the switch has failed, or an electronics component has gone duff. I have a Tascam TG-7 tuner that did the same thing. Unfortunately, the switch is good, so there's something else causing it not to shut off. You will likely have to get the preamp/tuner replaced.