How did u know if the starter is bad?

Have qualified personnel clean ALL battery cables - there are two positive cables that especially must be CLEANED.. Then clean em again!

Agree with push rod. Check your battery terminals to see if they are dirty. A white crusty material forms on the battery terminals and connectors. You can use a special cheap tool made just for cleaning the battery terminals and connectors. Or you could use baking soda to dissolve the acid which is what that white crusty substance is. They make special product to put on the terminals it is like a grease to prevent corrosion build up. If the battery terminals are clean and tight the next thing to do is take your battery to the auto parts store and have them test your battery to see if it is good. If the battery is verified good and the terminals are clean then you can start to suspect the starter. Simply put the starter when failing will be hard to start eventually it won't start at all.