Low battery capacity after calibration (102% -> 92% -> 85%)
Recently, I bought a new battery (twice) for a MacBook Pro Retina 13” (Early 2015) that was given to me and had a blown battery. The OS is an up to date Catalina. The battery was purchased from an Apple centric webshop in my country.
Immediately after installation, the maximum capacity was reported as 102% by Coconut Battery. Interestingly, both batteries report the same serial number and battery age (605 days). Cycle count of both batteries was 1 after installation. Since the iFixit guide recommended to calibrate the battery I went and immediately did so.
The result was, with both batteries, that there was a sharp maximum capacity drop after each calibration. I’ve tried draining it as slowly as possible, yet to no avail. After two calibrations the displayed maximum capacity was 87% / 86%. This is congruent with the output of “system_profiler SPPowerDataType”. The maximum capacity also varies by up to 6% depending on current load. I also notice that there are 3-4 drops of 3% displayed current capacity when draining the battery. Maybe cell switches? I don’t know.
Also, there’s a discrepancy of up to 5%, diminishing the more the battery is drained, between actual reported current capacity and the OS X display. This I gathered is normal.
Admittedly, I am confused. Did I get two bad batteries? Is this is a display bug in OS X since the runtimes still seem very high to me? Additionally, I’ve run “ioreg -l w0 | grep “BatteryData”” and now I wonder what the QmaxCell values of “6199”, “6237” and “6259” mean. Averaged, those result in a ~95% maximum capacity.
Furthermore, the “Amperage” value is reported as “18446744073709551398” which seems nonsensical to me. “PMUConfigured” is set to “0” - unsure what this means; excerpts from other people on the net show various values here.
I’ve also reset PRAM and SMC just to be sure.
I’m posting here in hopes that someone here has enough knowledge about the inner workings of the batteries in MacBooks. Any help would be greatly appreciated.
EDIT: Sorry for all the edits - just adding bits of info.
EDIT2: I’ve let the battery drain to 18%, and I’ve noticed that, starting from ~20%, the maximum capacity would start diminishing. After plugging in the charger, it shortly displayed 78%, and now sits at 84%! Something is definitely up here, and I don’t think it’s the battery (cells) that’s bad as such…
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