Ring Doorbell 1st Generation

Hi Everyone: Hope everyone in the community here and your families are doing well. I purchased my Ring Doorbell 1st Generation 4 years ago. It came with the instruction manual, which I just downloaded to make sure it was the same one, and it was. The instructions said if I was replacing my existing doorbell, I needed to shut the power off because I would be attaching my Ring to the wires inside the door and so I did just that. I followed every step in the instruction booklet and when the last step was done, it said "I was done." Today, after 4 years, when my son came to the house and rang my bell, I didn't hear it. So, I went into the app on my phone and it indicates my "battery life is low" I can tell you right now that if you are able to download the manual for this doorbell, you will see that nowhere in the manual does it mention a battery anywhere. So I am hoping that someone will let me know why I am getting this after 4 years of it working perfectly and where in the manual does it say anything about a battery and where it is because if I connected it to the wires from my original doorbell, I'm pretty sure it was a "hard wired" installation. However, after speaking with customer service this evening, I was told it is not hard wired and it's a battery operated doorbell and it was a miracle that it didn't need charging for 4 years. Any help you can give me would certainly cause a lot less stress right now. Thanks, in advance, for your help and I look forward to a reply. Kind Regards, Anita