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I think you're remembering incorrectly. I don't see how the addition of memory, even doubling it, would result in a 50% decrease in battery life.
i use my macbook on battery for classes. ive been using it the same way the entire semester and on wednesdays, i have classes from 8-5. when i first got the macbook, i was able to go through the day without bringing my charger. now its able to get me through about 3 hours before it dies.

strange, oh well

in terms of performance, it has really improved. i hardly ever get beach balls now whereas before, i did with a new computer.
 
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