Macbook Air vs Macbook Pro - Battery/Graphics Question

We have an older MacBook Air with an ailing battery. We just got a new one ordered from Apple, but the person at the Genius bar suggested my wife might need a MacBook Pro for what she is doing instead of a MacBook Air. My wife is an adjunct professor and teaching a three hour class each week where she uses the Air to project on to a big screen. Here presentations are doing in PowerPoint and they have a lot of graphics and video embedded. Apparently without an extension cord there is not access to a plug and her battery stopped lasting through the class. The person at the genius bar stated that because the Air doesn't have an independent (not sure the exact words he used) graphics processor this puts too much strain on it to project on to another screen and therefore she should get a MacBook Pro. To me this sounds a little excessive, but would love to hear other folks thoughts. I think the issue is more that the Air is old (5 or 6 years old) and not that it is not powerful enough to project a powerpoint onto an external screen. My guess is that buying a new Air should be sufficient, but would love to hear thoughts from the experts.