Strongly recommend you take it back to the shop you bought it from and see if they can give you a discount on repair. Hopefully, it is still under warranty.
The camera battery is not user-replaceable I have not heard of any successful replacement. However, if you are stuck because you can't take it into a shop, then as a last resort, you may want to look into what this community member did. If you get it to work, please post the method that works for you to help other people.
Unverified and Will Void Warranty
・PANASONIC-----VW-VBX090-W / VW-VBX090
above all are the battery equal to DB-110, except capacity.
This battery is $7.99 with free shipping. it is NOT VERIFIED that it works.
These are instructions on taking apart the THETA.
The camera is not designed to be taken apart.