Welcome!
So battery is replaced a some of the keyboard letters don’t work like J for example.
First:
- Have you blown out the dust around the keycaps?
- Did you test with an external keyboard? If there were no issues with a known-good external board, that suggest the internal one is damaged
- If an external board works, try an SMC reset
Otherwise, keyboard issues are, in a way, expected after a battery event. The swelling battery can damage what is above in addition to what is below. Although not directly above the battery in that model, the keyboard board was likely stressed while the battery was swollen. Based on long history here, swelling batteries can damage both keyboards and trackpads.
If it is physical damage, no amount of system software manipulation or resets will change that.
If you can, check the trackpad as well if you can. Once compromised, they can show unexpected behavior including skipping and delayed reactions.
In the US, PowerBook Medic lists parts for most old Macs. A caveat: after the pandemic, their inventory seemed greatly depleted, but that may be a resource. I've not worked on a plastic MacBook so please check some take-apart sites to research the "hows" and the "don'ts" of working on one. We are not allowed to post links here to take-apart sites.
I looked at one repair site for that model and found two discouraging things:
- The keyboard appears integral with the upper case
- The upper case can only be accessed by removing almost everything inside the computer.
A gutting like that can put other parts at risk if you are not comfortable inside a computer with tiny parts and connectors. As much I as encourage keeping old Macs in service, I must admit this one may be beyond practical repair.
