An S21 Ultra that will not charge has had five years of plugging in, so the USB-C port and the battery are the first two suspects. The phone takes 25W over USB PD, so a modern phone charger is fine, but a cable that works at one angle means a worn port, and a phone that charges to 100 and dies in an hour means a worn cell. Clean the port with a wooden toothpick, swap the cable, then run the battery test in Samsung Members.
Differential
Likely causes of “Samsung Galaxy S21 family will not charge or charges slowly”, and how to tell them apart
- 1
A worn USB-C port
What separates it The cable works only at one angle or falls out
How to confirm Lift lint out with a wooden toothpick and try a second cable
- 2
A worn battery
What separates it It charges but the percentage falls fast or it shuts off at 30 percent
How to confirm Samsung Members' battery test reports the cell
- 3
Protect battery at 80 or 85 percent
What separates it It stops before full
How to confirm Turn it off in Settings, Battery to charge to 100
- 4
A swelling cell
What separates it The back lifts or the screen gaps
How to confirm Stop charging and go to a repair center
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the cable works at one angle only
- The charger's wattage
- The battery test result
- Whether the back or screen has lifted
Try in this order
0 of 3 completedClean the port
ReversiblePower off, light the USB-C port and lift lint out with a wooden toothpick.
Swap the cable and charger
ReversibleUse a known Samsung cable and a wall outlet.
Check Protect battery
ReversibleOpen Settings, Battery and look for the 80 or 85 percent limit.
Model-specific
What is true of this model and not of its siblings
- Charging
- 25W wired, 15W wireless and 4.5W Wireless PowerShare, per Wikipedia.
- Charger not included
- Samsung stopped including a charger with the S21 series, so a slow or no-charge fault is often a weak third-party charger or a worn cable; test with a known Samsung 25W charger first.
- Other models this page answers
- These steps also fit the Galaxy S21.
Stop boundary
When this stops being a self-service repair
- !If it will not charge on a known charger and a clean port, contact Samsung or a repair center
- !If the back lifts, stop and go the same day
Evidence ledger
Sources behind this answer
Exact questions
Common questions
How fast does an S21 Ultra charge?+
Wikipedia lists wired charging to 25W over USB PD and Qi wireless to 15W on the S21 family.
Should I repair a five-year-old S21 Ultra?+
Samsung's US list shows $269 for the module with a new battery and $229 for the screen alone. The phone no longer gets security updates, so weigh the price against a newer phone.
Why does it stop at 85 percent?+
Protect battery. It limits charging to 80 or 85 percent, and turning it off in Settings, Battery allows a full charge.
How do I see the S21 Ultra charging speed?+
The lock screen names the mode, with Fast charging for the 25W rate and Charging for a slower one.
Why does the phone shut off at 30 percent?+
A worn battery can no longer deliver the current the phone needs when the charge is low, so it shuts off early. A battery test in Samsung Members reports this.
Does the Galaxy S21 Ultra come with a charger?+
No. Samsung dropped the charger from the S21 box, so many owners use an older Samsung charger or a third-party one; a USB PD charger of 25W with PPS gives the phone's fastest rate.
Can I use a phone charger from another brand on my S21 Ultra?+
Yes, if it supports USB Power Delivery. Without PPS the S21 Ultra charges at a lower rate; a Samsung charger gives the fastest rate.