iFixit has a guide for replacing the top screen, after a cursory read through it looks to be a little challenging as Nintendo applied glue liberally throughout the device so do be careful. New Nintendo 2DS XL Top Screen Replacement If you do not want to follow the guide and your DS is out of warranty I know in my area local computer shops are capable of fixing hand held devices like that. If your device is still in warranty either contact the store you bought it from or go to Nintendo’s warranty site.
There is a cable that connects the home button to the mobo in the phone that probably got pinched or took some form of damage when you applied the new screen, you will have to take the screen back off and replace that cord or the entire button.
I unfortunately am no mechanic but things I would get tested are your (1) Fuse for the gauge itself (2) The gauge functionality as those fail from time to time (3) Or you have a clogged heater core which may inhibit the gauge from working I apologize that I am not certified to give you more concrete answers.