I bought a used HP EliteBook 840 G1 and was told its battery health was about 89% of the original capacity, with 109 charge cycles. The original design capacity is 62 Wh and the reported full-charge capacity is around 55 Wh.
After installing Arch Linux, btop estimated roughly two hours of battery life and showed power usage around 15.8 W. Linux reports the battery's current energy as approximately 46 Wh, even though it displays the battery as 100% charged. The same value appears in /sys/class/power_supply/BAT0. HP's built-in diagnostics reports a 62 Wh design capacity and a 55 Wh full-charge capacity, which seems reasonable.
I have tried adjusting power settings and using powertop, but the readings did not change much. Is the battery actually degrading unusually quickly, or is Linux simply reporting the current charge differently from the full-charge capacity? Could recalibrating the battery after installing Linux correct the percentage or runtime estimate?
2 Answers
That sounds normal rather than like a battery that suddenly lost another 9 Wh. The 55 Wh figure is the battery's estimated full-charge capacity, while the 46 Wh figure is the energy currently stored. If Linux says that 46 Wh is 100%, its battery gauge may be using 46 Wh as the current maximum, or the reading may have been taken before the battery was truly topped off. Also, 15.8 W of power usage would give roughly 3 hours from 46 Wh, so the estimate is at least mathematically plausible. Let the battery charge fully, then compare the actual runtime instead of judging it from one reading.
A calibration cycle may help the percentage estimate, but it will not restore lost physical capacity. Charge it to 100% and leave it plugged in for a while, use it normally until the system reaches its low-battery shutdown level, then charge it back to full without interruption. Avoid doing this frequently because deep discharges add wear. The important values are design capacity versus full-charge capacity: 62 Wh versus 55 Wh is about 89%, which matches the seller's claim.
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