Old Apple Watch battery replacement in Tokyo?

Hi all,

I live in Tokyo and would like to have the battery of my Apple Watch Series 4 replaced because it won’t last half a day.

Since the watch itself is pretty old, do you have any suggestions as to where to have it done without spending too much money? It wouldn’t make sense if the battery costs more than the watch itself…

I would like to keep using it rather than purchasing a new one to be honest, as it lacks nothing for what I need.

Thank you in advance!!