Mountain Lion and Battery Capacity

I know that there has been much discussion about Mountain Lion and how quickly your laptop battery runs down when running it.  But most of the discussion seems to assume that ML is consuming more power than its predecessors.  I am starting a new thread because I wanted to suggest a different idea...

 

I'll start with a full disclosure - I have a five year old 15" MacBook Pro that has 4GB RAM.  The battery has been fading gently over the years and the system has been telling me to service the battery for at least a year.  I have not bothered because it all still worked for the ways that I use it.  I thought that it was poor that after only 283 cycles I had 50% capacity when the usual measure is 80% after 300 cycles but hey, that's life. As I say, it still worked for how I use it and that is the important thing.

 

I upgraded to Mountain Lion last week (from Snow Leopard) and the battery life has plummeted.  Using CoconutBattery the problem seems to be how ML measures the battery capacity.  Snow Leopard reported that I had 50-60% of the design capacity in the battery.  ML reports that it is 20% or less.

 

So, for me, it looks like ML is measuring a much lower capacity in the battery.  Right now it thinks that I have 13% of the design capacity, fully charged my battery holds only 710mAh - that is not going to translate in to a lot of time away from the mains.

 

I did try to reset the battery using the approved calibration routine.  Usually (under SL) , if run until it shuts itself down and then left on sleep overnight, the battery is fully discharged in the morning (and the sleep light has gone off).  After being left last night the sleep light was still happily on - ie there was enough charge left in the "fully discharged" battery for it to sleep through the night, which is unusual.

 

So, I think that I am getting a poorer battery experience because ML is measuring less capacity in the battery.  It thinks that there is 710mAh instead of the 2500mAh that SL measured.  That means that each 1% of battery is only 7.1mAh instead of 25mAh, so each % is used up much more quickly and the battery life is much less.

 

Assuming that the extra 1790mAh that SL measured is still there it also explains why it was able to sleep all night on what should have been a fully discharged battery.

 

The question for Apple is why does ML measure a lower capacity and how does it fix it...

View the original article here