Laptop battery charging stuck at 90%

My laptop battery charged week ago up to 100% (fully).

Recently, I noticed (within this week) that it now charges only to 90%. First sign was that laptop battery led now always orange (charging) and never reach green (charged) when plugged. Charge without OS running never reaches green led too.

Linux (3.18) reports 90-93% charge when it reaches the level when it does not want to go up to 100% now.

Some more relevant information from kernel:

% cat /proc/acpi/battery/BAT0/state
present:                 yes
capacity state:          ok
charging state:          charging
present rate:            0 mA
remaining capacity:      1611 mAh
present voltage:         12038 mV
% cat /proc/acpi/battery/BAT0/info
present:                 yes
design capacity:         2250 mAh
last full capacity:      1759 mAh
battery technology:      rechargeable
design voltage:          10800 mV
design capacity warning: 176 mAh
design capacity low:     18 mAh
cycle count:          0
capacity granularity 1:  22 mAh
capacity granularity 2:  22 mAh
model number:            X101CH
serial number:
battery type:            LION
OEM info:                ASUS

I also remember that /sys/class/power_supply/BAT0/voltage_now reported 12.6V (4.2V per cell) for 100% battery, but now it only reaches 12.04V (4.01V per cell). /sys/class/power_supply/BAT0/current_now shows 0.

My battery design capacity is 2200mAh 10.8V 23Wh. My battery age is 2.5 years. Is this a sign of battery degradation? Do I need to worry about that?

EDIT: I remember before the "fall" last full capacity was about at 2050mAh and did not degrade much (by 300mAh at once or during 2-3 days) earlier. (I monitored it for a while with script)

Answer

This is a sign of battery degradation. If you look at the cat output, design capacity of your battery is 2250 mAh while the last full capacity is 1759 mAh. That's approximately a 21.8% degradation of battery life.You should perform a battery calibration to ensure that you have current and accurate information about battery wear.

Basic Calibration Instructions

Calibrating — or recalibrating, really, as the battery was calibrated in the past when the battery had more capacity — involves letting the battery run from 100% capacity straight down to almost dead, then charging it back to full. The battery’s power meter will then see how long the battery lasts and get a much more accurate idea of how much capacity the battery has left.

Source: howtogeek.com