when do i need to Change battery on my Mac?

appleicontopleft > About This Mac > System Report > Power ... when "Condition" is not "Normal"

Also ... on occasion the battery swells inside the case, pushing out the bottom and damaging the trackpad and keyboard. This has been seen enough to know it occurs but is not common.

gattus006 wrote:

when do i need to Change battery on my Mac?

When it is no longer doing its job. There is no schedule. I have a couple MacBook Pros about a decade old and have never experienced any battery issues.