New battery in the alvarez/yairi

I put a new 9-volt battery in my Alvarez/Yairi acoustic/electric guitar yesterday. I rarely use the built in tuner, so I hadn't really noticed that the battery was going bad. And I don't know if it has an effect on the functions or not - but I would assume it does. I did think it sounded a little odd the last couple of weeks. Anyway, yesterday I was going through the songs for Sunday in my office and it was out of tune pretty bad (winter is such a hassle), so I decided to tune with the built-in. It wasn't working right, and so I changed the battery. There are just two screws that come out and then the whole assembly comes out. I haven't checked the sound through the amp yet, but it certainly made a difference in the light on the tuner. I suppose I should check that more often. I don't even remember the last time I changed it. I'm sure it has been several years.