Check battery usage before replacing the battery. An app using power in the background, a weak cellular signal and a recent update can drain a healthy battery. Compare idle use with active use, then check the battery-health information available on the exact model.
Differential
Likely causes of “Samsung Galaxy S battery drains too quickly”, and how to tell them apart
- 1
A worn battery at five years
What separates it It falls from full to empty in a few hours, runs warm and shuts down at 20 to 30 percent
How to confirm The 5000 mAh cell has had roughly 1,800 charge days; Samsung Members' battery test reports its condition
- 2
A swelling cell
What separates it The back panel lifts, the screen gaps at an edge or the phone rocks on a table
How to confirm Stop using it; a swollen lithium cell is a fire risk and needs a repair center
- 3
No more security or optimization updates
What separates it An app misbehaves and nothing in Settings, Battery explains it
How to confirm With support ended the phone gets no new fixes, so remove or replace the app
- 4
The 5G radio in weak signal
What separates it Drain is worst in a building with one bar
How to confirm Compare an hour on Wi-Fi with an hour on LTE
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the back or screen has lifted at any edge
- The Samsung Members battery test result
- Hours of screen-on time now against a year ago
Try in this order
0 of 3 completedLook at the phone
ReversibleSet it on a flat table. A rocking phone, a gap at the screen edge or a raised back panel means a swollen battery; stop here and book a repair.
Check the top of the battery list
ReversibleOpen Settings, Battery. Put heavy apps to sleep under Device care, Battery, Background usage limits.
Get a quote
ReversibleAsk Samsung or a repair center for a battery replacement price.
Model-specific
What is true of this model and not of its siblings
- Samsung Galaxy S21 family battery drains too quickly
- A Galaxy S21 Ultra is over five years old and Samsung has ended its software support. Its last major update was One UI 7 on Android 15 and its final scheduled security update came in November 2025, so a battery that now drains fast is almost always the cell itself, not a setting. Check the battery first: run the battery test in Samsung Members, look at the back for a bulge, and get a replacement priced. Samsung's US list shows $269 for a module repair with a new battery on the S21 Ultra and $229 for the screen alone.
- Battery
- 5,000 mAh with 25W wired charging and 15W wireless charging, per Wikipedia.
- Other models this page answers
- These steps also fit the Galaxy S21.
Stop boundary
When this stops being a self-service repair
- !If the back bulges or the screen lifts, stop charging and go to a repair center the same day
- !If the battery test reports a fault, get a battery replacement quote; Samsung's US list shows $269 for the module with a new battery
- !If the phone is worth less than the repair, plan the replacement phone now, because it no longer gets security updates
Evidence ledger
Sources behind this answer
One UI 7 as the last update and the end of security patches.
Which S21 models were left with updates.
An owner's swollen S21 battery.
S21 battery, charging, chip by region, storage, Wi-Fi, display, glass and back panel.
Exact questions
Common questions
Is the S21 Ultra still getting updates?+
No. Android Headlines reports One UI 7 on Android 15 as its last update and TechRadar reports Samsung ended support for the S21 series, with the final regularly scheduled security update in November 2025.
How much is an S21 Ultra battery replacement?+
Samsung's US list shows $269 for the module repair with a new battery and $229 for the screen alone; prices vary by store.
What are the signs of a swollen battery?+
A back panel that lifts, a screen that gaps or bows from the frame, or a phone that rocks on a flat table.
battery drain: model differences
Also covered: Samsung Galaxy S20 Ultra family.