In real terms tennis ball machines have only been with us a short while, Rene LaCoste was credited with creating the first tennis ball machine in the 1920s. Forever trying to improve his game LaCoste invented a hand crank tennis ball machine which was fired by a partner at the opposite end of the court.
In the early 70s Bob McClure created what is regarded to be the first commercialy viable mains powered tennis ball machine by reversing the motor of a vacum cleaner to build up enough air pressure to fire a tennis ball out of a launch tube, this tennis ball machine was named the "Little Prince". After the machine became successfull Bob McClure built the company Prince Manufacturing.
The pneumatic tennis ball machine reigned supreme for some time as the only viable option until companies such as Sports Tutor bought counter rotating wheel technology onto the market. Although appealing battery tennis ball machines were not successfull at first due to short running times, but as technology has improved so have the running times and now because of their portability battery tennis ball machines are favoured more strongly over the mains tennis ball machines by coaches and players alike, that said mains versions are still very strong in the market place for players with their own courts and for health clubs who do not want to bear the cost of replacing poorly treated batteries. You can find a bit more history by clicking here