Can anyone explain Genius Bar's battery diagnostic tool?

Basically the green indicates a good battery, the yellow indicates a consumed battery (cycle counts have exceeded the rated number allowed) and the red indicates a battery that has failed.

If the dot ends up in the green then it is deemed to be operating within reason and is considered to be good without need for replacement.

If the dot ends up in yellow then it is deemed to be "old age" for a battery, maybe with a cycle count of 400 when the battery is only rated for 300 (these numbers vary between models). If the battery is showing signs of failure or weakness but is in the yellow then such failures/weakness are somewhat expected due to the age or amount of usage the battery has experienced.

If the dot ends up in red then your battery has likely failed prematurely. I forget the percentage but the test has basically found that it's capacity is lower than X% of it's original capacity even though it's under the rated cycle count. For instance, if your battery is rated for 300 cycles but only has 10% of it's original capacity despite only having 150 cycles then it will fall under the red.

As far as the x/y axis location of the dot, I believe you're correct.

Hope that helps. In defense of the Genius/employee, battery related issues are very hard to deal with/explain. Everyone has different usage habits, everyone has different perceptions of how the battery should perform, etc. This diagnostic looks at capacity & cycle count, the only two real metrics you can actually measure with a battery. You "could" request that they check in your Mac and run an extended battery test on it (usually putting the Mac under light stress and timing how long it takes to completely drain while under Genius supervision, but more than likely they would default back to the results of this diagnostic. It looks like you're right on the edge, you might check back with them in a month or two.

g35 said:

Tat its current rate I'm guessing it will drop into the red before it reaches the yellow. I hope the genius will not attribute the battery performance to heavy use when my cycle count really doesn't reflect that.

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I wouldn't worry too much, that test is a quick way for Genius' to see if a battery is good, bad or consumed. Beyond that they typically don't put much thought into it unless the customer has had a multiple bad batteries or if there is some other related issue at hand. Basically, if they see red and the Mac is under warranty then it would be more work for them to argue against replacing the battery than to just replace it.