Confused about Ring Doorbell 4 and existing wiring

I have read through the help pages and some support forum topics here, but I remain a bit confused. I'm looking into buying a Ring Doorbell 4 with battery, but I also have an existing doorbell with wiring. If I remove the existing doorbell and attach the wiring to the Doorbell 4, what is the exact purpose of the wiring? Will it require me to still recharge the batteries after a certain amount of time? Or will the wiring allow the Ring to "auto-charge" via the current wiring? i.e. battery would only kick in if the power in the house goes out? And / or will the existing wiring allow me to still hear my existing doorbell chime? Or would I need to buy the optional Ring Chime to be put near the front door to be able to hear when someone's at the door (not taking into account ringing on my phone for now) Or put differently, what Ring product would best fit my needs to: - re-use my existing house chime (if possible at all) - attach to my existing wiring - optionally have a battery, but not required - allow a Ring Chime to be put in my garden office (which has wifi), so I can hear someone at the front door there