Having issues with my mmi working.

Background info....daughters car was leaking oil. So we took 3 wks to replace the head gasket. During this time of course you can't turn car on so it went dead...we had to jump it but lights and dashed just flickered even when we took the key out so, it didnt work. We had to let it sit hooked up to battery tender for 24hrs. Finally we got it started but had to keep jumping it for days until the battery was charged. During this time the mmi wouldn't work and we thought maybe it was cause the battery was so dead. After a week we took it to get the battery tested and auto zone said it's good to go. So why was the mmi having issues. Then all of a sudden it started working on and off...but not consistent enough. Now it's maybe once a week. We have tried a hard rest on it and checked all the fuses in the 3 different spots. Everything looks good.

Any other ideas on what's wrong or what we could try?