Does the real-world MacBook Pro battery life scale linearly with it's capacity? I have a well-worn battery on my 2010 MacBook Pro. After 467 charge cycles, I get about 3 hours of the normal 6-7 hour range.

Using coconutBattery shows me that the charge capacity is 5783 mAh, compared to the original 6900 mAh. Extrapolating the math there would indicate that a replacement battery would only last for an additional half an hour!


Is this number a reliable indicator of present and future battery life?
What kind of realistic usage am I likely to get from a new battery under Lion?


(For what it's worth, I've already calibrated the battery with a full drain, checked for rogue background processes, and force-disabled the NVIDIA graphics with gfxCardStatus.)
First of all a note, coconutBattery is a tool which helps you indicating a battery problem. It's measurements are not 100% accurate...

If you really want to know the health of your battery, I suggest you take a look at System Profiler (Applications &lt; Utilities &lt; Sytem Profiler) and open the 'Power' bar. Here you see information comming directly from Mac OS. It could be the same as coconutBattery, depending on what version you use, but this is the most reliable information about your battery...

You have Charge Information and Health Information  

  

And to answer your question, I don't think their is a strict correlation between the lifetime of a battery and the number of mAh left (at least none that I found of). There's been a lot of writing about batteries, their lifespan and their health. But it depends on so much external factors, you can't make a decent prediction of it.
As your Mac ages, you battery's health will go down. Learn to live with it :)