strange battery draining at 20%

[stvs]

hello. my device is the xperia e4g and i have unistaled all the bloatware and made it super "slim"
no facebook,google store,gmail, gps etc.
so from time to time i play only chess,without any other app to run at same time.
the bettery drains normaly and its very very good(only after several hours of play can reach 20% from 100%)
until 20% the battery is super.now when reach the "magic" 20% something strange is happening:
shows a warning window saying your battery is low etc,and suddenly drops fast from 20% to 15 10 and 5%
within 2 mins! and shut down.the device is a little warm but not hot (summer here,room temp 25c with A/C on)
so when i charge it after 2-3 mins its shows 22-23% !!!.today i made a factory reset to see what will happen again.
notice:during the winder when reached 20% the only effect was a perfomance decrease to save battery time.
seems this device has a battery limit at 20% ,but why on the summer this fast draining?

 

[Hadron]

If it consistently happens at 20% it might be a battery calibration problem.

But with an old battery it's not uncommon for charge measurements to be unreliable. My phone is older than yours (more than 4 years), but I regard anything below "30%" as "at risk" now. Sometimes it will behave normally below that, sometimes it will drop rapidly (25% -> 20% -> 15%, ->10% -> 5% -> dead, not actually in 5% increments), sometimes it will simply shut down at 15%, or 27%, or whatever.

 

[stvs]

If it consistently happens at 20% it might be a battery calibration problem.

But with an old battery it's not uncommon for charge measurements to be unreliable. My phone is older than yours (more than 4 years), but I regard anything below "30%" as "at risk" now. Sometimes it will behave normally below that, sometimes it will drop rapidly (25% -> 20% -> 15%, ->10% -> 5% -> dead, not actually in 5% increments), sometimes it will simply shut down at 15%, or 27%, or whatever.

yes i suspected battery caalibration issue,so you suggest battery calibration,can you give me some good
information how can i make a good calibration?

 

[Hadron]

The simplest recipe you'll find is to let the phone discharge until it shuts down, charge it fully, then let it run all the way down again. It's not actually good for a battery to do this regularly, but it's similar to a procedure that my laptop's manufacturer recommends occasionally for calibration purposes so there's a fair chance there is some validity to the process. Don't do it too often, but it won't hurt to give it a shot once.