Battery Calibration: A (Sometimes)-Effective Cure For Charge Castration

Last Friday morning, I happened to notice something strange with my MacBook Air’s power subsystem; although the menu bar indicator reported that the battery was only at ~75% of capacity, it wasn’t charging. Repeatedly disconnecting and reconnecting the power adapter produced no relief. When AC-tethered, the system would run fine. It’d also operate (for a while, at least) when on battery power, but the stored charge would steadily dissipate, and I couldn’t coax the system into replenishing the batter once I re-tethered the AC connector.

I tried resetting the SMC (System Management Controller), which had resolved a conceptually similar problem in the past. No dice this time. Nor did resetting the PRAM (Parameter Random Access Memory) do the trick. I was a bit bewildered, until I looked closely at the screenshots from the ‘power’ section of the System Profiler report:

along with the even more informative output of coconut-flavour’s coconutBattery utility:

Note that the reported Current Battery Capacity (i.e. Full Charge Capacity) is higher than the Original Battery Capacity? While I’d love for this increase to be true, especially for a system design in which the lithium-ion polymer battery is annoyingly embedded and therefore not user-swappable, reality is contrary to what coconutBattery was suggesting. The more you recharge-cycle such a battery, the lower its maximum charge capacity is.

Admittedly, I hadn’t stringently followed Apple’s suggestions to cycle the battery and thereby fine-tune its associated sensing circuitry on a monthly basis. Based on the above discrepancies, calibration seemed to be my next step. With the assistance of a long-running Hulu video, I drained the battery to the 0%-remaining point where the system automatically went into hibernation. I let it sit disconnected from AC power for the next six hours. I connected it to the AC adapter, thankfully saw that the MagSafe connector LED switched from green to red, and let the MacBook Air recharge overnight. And when I woke up the next morning, here are the encouraging results I found:

The reported Current Battery Capacity (Full Charge Capacity) was now at a reasonable percentage-of-original value considering the battery’s age and number of charge cycles it’d experienced to date. And the battery seemed to be properly recharging back to 100% every time I connected it to the AC adapter. I thought I was good to go…

…until Sunday morning, when the same unable-to-charge behavior occurred as two days prior. I went through the same tedious steps as last time; draining the battery, waiting, then recharging it. And this time, I followed them with resets of the SMC and PRAM. This morning, the capacity read 100%. I disconnected the system from AC power for 15 minutes, reconnected it, and the battery recharged as it should. I thought I was good to go…

…until this afternoon, when I ran the system on battery power for several hours, reconnected it to external AC power, and it again refused to charge:

As you can see, completely draining it once again has prompted recharge to reactivate:

But I clearly can’t rely on the MacBook Air to operate in a reliable manner right now. Fortunately, I’ve got AppleCare service for another ~1.5 years, so I’ll be making another trip to the Reno Apple Store tomorrow evening (I wonder how long they’ll hold onto it this time?). A replacement battery and a replacement logic board are the two likely resurrection candidates, so says my research.

Have I mentioned how much I detest non-user-replaceable batteries?