What is the difference between 9v1 and 9v2 batteries?

Well, darling, the only difference between a 9v1 and a 9v2 battery is the capacity. The 9v2 battery simply has a higher capacity than the 9v1 battery, meaning it can last longer before kicking the bucket. So, if you want your device to keep on truckin' without needing a battery change as often, go for the 9v2.