I was exclusively a PC man (specifically Dell, Gateway, and HP), but I am now planning to buy a Mac, because my sister has a Mac, with a battery life (much) longer than mine, and I would like to benefit from that. Could anyone suggest the best Mac to buy if I want the longest battery life possible. I mean really the longest, even if it sacrifices other things to achieve it.
According to Apple's website, the 13" MacBook Air and all of the MacBook Pros have 7 hours of battery life. This means that there are seven laptops for you to choose from: Four 13" computers, two 15", and one 17". The possibility of getting more than 7 hours exists, because this number is determined in this manner:
The wireless web test measures battery life by wirelessly browsing 25 popular websites with display brightness set to 50%.
—Apple (at the very bottom of the page, point number 2).
My experience is the entry level 13" MacBook Air is quite miserly, but no where near the battery runtime of the enormous 17 inch MacBook Pro. Even with a high end GPU and CPU - it has so much power it's the winner for all day performance according to people I know that have them.
The current 15 inch MacBook Pro are a bit more power hungry than the ones of the mid 2009 vintage - so if you can wait, many are speculating whatever new Ivy Bridge based MacBook Pro eventually gets released will likely be less hot (and get better battery life) than the current CPU/GPU lineup. If you can't wait and need, need, need all day battery life - I'd pick up a used Mid 2009 or early 2010 model and just watch the CPU to make sure you quit programs that will reduce it from 10 hour life down to 5 to 7 life at a more active CPU load. The nice thing about the older mac is you can pin the GPU to the integrated one and know it will be miserly with the power.
Now if I don't take your question literally, but wholistically - you should get a $399 iPad and the $999 MacBook Air. Together, they are a potent combination for Netflix and productivity - I could see you getting 10 hours of netflix and 5 hours of laptop life in "one charge"
It depends on what you mean by "battery life". Charge capacity will decrease over the usable life of the battery, so if you mean "max charge capacity", @Mahnax gives you this information above.
If you mean longest usable life, this is largely dependent on usage patterns. Different factors play into usable life, as this article points out:
The key point of this article is that you should use (read: disconnect from AC power) your battery a little bit every day to get the most usable life out of it.