Does the MacBook Pro have a better battery than the MacBook Air?
No, MacBook Air has more battery life than the MacBook pro. MacBook pro being more powerful than the MacBook Air consumes more battery than the MacBook Air. In MacBook Air Apple claims a battery life of 12 hrs but you can get up to 9–10 hrs of battery life easily while surfing and using iTunes whereas for MacBook pro company claims around 10 hrs of battery life but you practically get around 7–8 hrs only.
Here's the link to the Apple website where you an get the full comparison of all the specifications of MacBook air and Pro.
Theoretically Yes but Practically Not. Because if you observe, MacBook Pro 15″(76 Wh) has more Wh battery than MacBook Air(54 Wh). But you have more power does not mean that you will get more battery backup. MacBook Air definitely gives better battery backup than 15″ MacBook Pro
MacBook Pro is much more powerful than MacBook Air, in terms of processor, RAM, Storage, GPU, display. So All these aspects get into consideration when you talk about battery backup.
MacBook Pro 15″ has faster processor, faster and more RAM, faster storage, faster GPU, better display and also has Touch Bar on it. Definitely you will use this MacBook for high end softwares, 4k editing, data analysis etc, So while performing these tasks, aspects mentioned above directly and indirectly drain battery more compared to MacBook Air. It is just like Classic phones(Nokia 3310, 230 etc) and Smart phones(Android, iPhones). Latest SmartPhones have more battery Wh(4000/5000 mAh) than classic phones(1200 mAh) but still Classic Phones give you more battery backup than Smartphones.
That's why still having more Wh, 15″ MacBook Pro gives lesser battery backup than MacBook Air as MacBook Air has slow speed processor, RAM, SSD, Basic Intel HD GPU, so Tasks which you perform on MacBook Air are light and do not consume much battery.
So Yes, it is true that MacBook Air has better battery backup compared to MacBook Pro.
No. It doesn't. This is because Macon air used low powered internals compared to the pro.