2529 Views 9 Replies Latest reply: Oct 26, 2008 10:33 AM by Charles Bortnick
Relax, it's fine. "Health" is determined based on the nominal value for a new battery; actual values vary. It's normal for the health to drop a bit at first, then stabilize. I'm at 123 cycles and 94% health. Since about cycle 20, my health has fluctuated between 86-96% (and it's been at the hig and the low end of that range in the last 10 cycles).
So, you have nothing to worry about. Apple spec is that a battery will maintain 80% health for 300 cycles; in practice, you can expect a useful life of 400-500 cycles or ~3 years, whichever comes first.
Don't forget to calibrate every couple of months:
Battery health is just a number for the cycle count and you can see the same info in Apple System Profiler under Power. It's a number based on the expected charge cycles the battery will take before it doesn't charge above a certain point, so it's a very rough figure to go by.
After about 300 charge cycles battery life may drop low enough that you start to feel like getting a new battery. 3 cycles are 1% of 300. This could explain why you are seeing 99%; after 9 days you probably have gone through at least 3 charge cycles. But battery meters can drop and rise daily, so don't be surprised if you see it report 100%, 99%, 99%, 98%, 95%, 97% 96%, 98%. If you obsess over it daily, you will probably go crazy.
That's precisely why the System Profiler grades the battery as good/regular/poor/check battery and avoids numerical values that can only confuse and unnerve the user. Worth noting is that iStat doesn't tell you what it considers as "excellent" health; at least CoconutBattery tells you that it considers 5600 mAH as the baseline for new Feb'08 MBP batteries, based on the serial number.
Sorry, Network23, but you're completely incorrect there. Health is calculated as (current full charge capacity / nominal new full charge capacity) * 100. Nominal new full charge capacity is 5556 mAh for a 15" MBP (rounded to 5500 mAh or 5600 mAh by different widgets for different batteries). Nominal new full charge capacity for a 17" MBP is 6300 mAh. "Health" does not factor cycle count into the calculation anywhere. Furthermore, health decline is non-linear.
Sorry, Network23, but you're completely incorrect there. Health is calculated as (current full charge capacity / nominal new full charge capacity) * 100.
Thanks for the clarification, you have a better formula than I knew about. I knew in the back of my mind that it wasn't just about cycle count but I let myself be misled by Apple's System Profile layout that lists cycle count as the only metric under Battery Health.
I stand by the main point of my post though, in that Battery Health is useful but not something precise enough to be obsessed about, and, as my number progression showed, the decline is non-linear as you said.
Thanks for the great answers gentlemen - I was starting to worry that I had a duff battery or worse still, a duff MBP!
All in all I'm VERY happy with my MBP and knowing it's working as expected just reinforces the the idea that I made a good choice to purchase one.
Now this battery question is sorted, any suggestions on good, fun widgets?
Cheers, thanks again
Glad you're reassured! I'll certainly agree with Network23's advice to not obsess over health numbers. My widgets are nearly all productivity-oriented (weather, traffic, package tracking, etc.) so those hardly qualify as 'fun'. The only exception is THIS ONE, but I'd recommend that only for Star Trek fans...