i have a 1998 nissan maxima and didt come with new battery, just wondering if anyone knows where id find what size and kinda i have to get or w/e it is idk anything about this...i guess basically what i need to know is what to tell the store im buying a new one from what i need...plz help

people have been telling me there is a book i can figure it out in in the store but im tryna buy mine online...and the battery i have now is not the right size so im stuck...any help is appreciated