I have a Toyota Camry in which the battery needs to be changed. Now I'm not the original owner and from what I know 1999 Camry can use both Group 35 and 26 batteries. Currently my car has a Group 35-6yr battery on it from ACDelco and I was wondering if it's ok if I put Group 26 battery on it? Will it be fine?

The two battery groups sold for your car are a group 35 and 24F. Don't use a 26 unless you are sure the terminals are on the correct side of the battery and the battery fits your tray. Also, make sure anything you buy has enough cold cranking amps for your winter.