Laptop problem

Hello, I'm having some issues with my laptop and wondering if anyone can advise/help me.

My laptop battery is not working, at all, I don't think it's even being recognised because my laptop says 0%. I've taken the battery out, checked for leaks or dust or bad connections but everything seems fine, so I'm thinking maybe the battery is just dead and needs replacing.

Does anyone know where I can get a new battery? Online or in a shop?
Anyone know how to fix it (if I'm wrong about the battery).

Thanks =)