# QuestionSlow charging on S21 Ultra

#### blackhawk

##### Senior Member
If the phone, battery, or charger start heating up, then, the charging rate will slow down.
I have a 1 Watt charger that I use for overnight charging. It takes it 1 hour and 20 minutes to charge by 10%.
Sometimes if it heats up too much I think it ends the charge cycle. Not for sure because I don't deliberately roast my batteries and will end it if it goes above 101F.

You can't do any wrong slow charging though as long as the battery temp is above 72F

#### nixnixnixnix4

##### Senior Member
Sometimes if it heats up too much I think it ends the charge cycle. Not for sure because I don't deliberately roast my batteries and will end it if it goes above 101F.

You can't do any wrong slow charging though as long as the battery temp is above 72F
If a battery takes 14 Hours to charge at 1 W, does it mean the capacity is 14Wh?

#### blackhawk

##### Senior Member
If a battery takes 14 Hours to charge at 1 W, does it mean the capacity is 14Wh?
No. V×A=W You don't know what the actual voltage or amperage is or how much is actually being stored by the battery and there's heat lose as well.

#### nixnixnixnix4

##### Senior Member
No. V×A=W You don't know what the actual voltage or amperage is or how much is actually being stored by the battery and there's heat lose as well.
In my case, it's a 5V 200mA charger.
Does that help?
There's got to be a way to make some kind of estimate or upper bound.

#### blackhawk

##### Senior Member
In my case, it's a 5V 200mA charger.
Does that help?
There's got to be a way to make some kind of estimate or upper bound.
You have to measure it real time as you charge it and adjust for the waste heat which may be slight enough to ignore in this case.
The voltage and especially current are likely not constant so you need to take that into account.

I wouldn't get too wrapped up in it... a watt hour meter on the AC side give you a rough idea and allow you to track changes over time.

#### nixnixnixnix4

##### Senior Member
You have to measure it real time as you charge it and adjust for the waste heat which may be slight enough to ignore in this case.
The voltage and especially current are likely not constant so you need to take that into account.

I wouldn't get too wrapped up in it... a watt hour meter on the AC side give you a rough idea and allow you to track changes over time.
But, assuming that a battery is taking in 1W for 14 hours with 100% efficiency: then, the capacity would be 14Wh?

#### blackhawk

##### Senior Member
But, assuming that a battery is taking in 1W for 14 hours with 100% efficiency: then, the capacity would be 14Wh?
You can't assume you need to measure it.
A more realistic way to gauge the battery capacity be to measure it's mAh output of a fully charged battery.

#### ione2380

##### Senior Member
All the smartphones I ever had resets the battery stats at 90% charge. S21 Ultra is the first phone I've seen to reset battery stats at 100%. That maybe means 100% isn't really 100% on s21 Ultra? I remember from my s9+ days when Samsung said that their phones are only charged 95% when showing 100% and the battery health will drop to 95% after 2 years of daily charges.

enigmaamit

#### enigmaamit

##### Senior Member
All the smartphones I ever had resets the battery stats at 90% charge. S21 Ultra is the first phone I've seen to reset battery stats at 100%. That maybe means 100% isn't really 100% on s21 Ultra? I remember from my s9+ days when Samsung said that their phones are only charged 95% when showing 100% and the battery health will drop to 95% after 2 years of daily charges.
It's quite possible. They give the option of recalibrating the battery on the Tab S7 to show 100% when it's actually 85% and once you toggle that setting, there's no actual way to tell by looking at the battery graph that you're running at 85% battery instead of 100%.

And they themselves say this prolongs battery life. So they're well aware of it and One UI already has to code to implement it.

Whether they've done it on the phones or not is the real question.

ione2380

#### chetly968

##### Senior Member
My phone never charges as fast as what's displayed in the lockscreen. It'll say 49vminutes til fully charged and takes 45-50 minutes. But doesnt bother me to much. As long as it's charging. This happens with every Samsung phone I own. Probably something with the wiring in my house.

#### blackhawk

##### Senior Member
My phone never charges as fast as what's displayed in the lockscreen. It'll say 49vminutes til fully charged and takes 45-50 minutes. But doesnt bother me to much. As long as it's charging. This happens with every Samsung phone I own. Probably something with the wiring in my house.
My 20 watt Samsung brick will fast charge with 60 VAC!
Had a pole line fault recently and saw this to my amazement before I realized the voltage had dropped out that low.
It's switching power converter has a -huge-voltage tolerance range.

Charging estimates are always off

#### nixnixnixnix4

##### Senior Member
We need a simple feature that should be quick and easy to add: bypass charging.
ASUS and SONY have it.
That bypass charging should also be added to Bixby Routines and made available to apps like Tasker, Macrodroid, and Automate.

Y'all want to make a change.org petition?
1 simple feature like this should be easy for them to add under battery settings.
And, Bixby Routines will allow us to initiate "bypass charging" and disable further charging once the battery hits a certain level.
Plus, if you connect your phone to a USB hub for DeX, it'll allow you to maintain the phone at 40-50% charge, initiate bypass charging, and then not have to worry about leaving the phone at 100% charge and degrading all the time.

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#### blackhawk

##### Senior Member
We need a simple feature that should be quick and easy to add: bypass charging.
ASUS and SONY have it.
That bypass charging should also be added to Bixby Routines and made available to apps like Tasker, Macrodroid, and Automate.
Problem being is it's easy to damage the charging cable and the c port with it tethered like that... just a matter of time.
It's also very inconvenient to use as such.

Life is easier when you except Li batteries are cheap and an expendable asset.

#### nixnixnixnix4

##### Senior Member
Problem being is it's easy to damage the charging cable and the c port with it tethered like that... just a matter of time.
It's also very inconvenient to use as such.

Life is easier when you except Li batteries are cheap and an expendable asset.
How would it damage the cable? You're just going to enable bypass charging via Bixby Routines at say 65% or 80% charge when the phone is on your night stand or desk.

#### blackhawk

##### Senior Member
How would it damage the cable? You're just going to enable bypass charging via Bixby Routines at say 65% or 80% charge when the phone is on your night stand or desk.
I thought you meant battery bypass ie using the phone powered by charger and not charging battery.
Charge limiting is fine if the phone's not on use.

#### nixnixnixnix4

##### Senior Member
I thought you meant battery bypass ie using the phone powered by charger and not charging battery.
Charge limiting is fine if the phone's not on use.
They call it "Bypass Charging" OR "Passthrough Charging".

#### chetly968

##### Senior Member
My 20 watt Samsung brick will fast charge with 60 VAC!
Had a pole line fault recently and saw this to my amazement before I realized the voltage had dropped out that low.
It's switching power converter has a -huge-voltage tolerance range.

Charging estimates are always off
The superduperuktra fast charging on my OnePlus 9 pro USB pretty reliable though which is strange.

#### blackhawk

##### Senior Member
The superduperuktra fast charging on my OnePlus 9 pro USB pretty reliable though which is strange.
The next jump in performance will be the graphene cells. Xiaomi already is using them.
Charge much faster and last many times longer than traditional Li's.

#### varcor

##### Senior Member
Your settings should match the photo. If you've adjusted the settings it should reflect Super fast charger connected. If it doesn't I would look to use a 3.0 Charging Cable. Beyond that it may need to be repaired.

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The question is not really if fast charging is bad for the phone, but more likely: why the hell is Samsung unable to manage fast charging on their premium and one of the most expensive phone whilst cheaper alternative works properly? If someone wants to have fast charge with detrimental effect on battery health in the long run, it is their choice and the option in the settings should enable that flawlessly... Which is not always the case
May have something to do with the Note 7 fiasco?

Once burned, twice shy...?

Dunno, I'm just guessing.
2
Everyone seems to know a lot about battery tech, but no one here seems to know why a feature (fast charging) that's supposed to work isn't working on a lot of devices.

With fast charging on, S21 Ultra should charge in ~75 minutes from 0-100 using a 25w Samsung charger as seen in many reviews. But that's not the case for some of us.

Does anyone know why? That's the question here.
I can understand your frustration buddy. But I don't know how to help. My 25W charger takes around 90 minutes to charge the phone fully. I've just made peace with that.
1
All the smartphones I ever had resets the battery stats at 90% charge. S21 Ultra is the first phone I've seen to reset battery stats at 100%. That maybe means 100% isn't really 100% on s21 Ultra? I remember from my s9+ days when Samsung said that their phones are only charged 95% when showing 100% and the battery health will drop to 95% after 2 years of daily charges.
It's quite possible. They give the option of recalibrating the battery on the Tab S7 to show 100% when it's actually 85% and once you toggle that setting, there's no actual way to tell by looking at the battery graph that you're running at 85% battery instead of 100%.

And they themselves say this prolongs battery life. So they're well aware of it and One UI already has to code to implement it.

Whether they've done it on the phones or not is the real question.
1
but why other S21 ultra charges faster?
Temperature is a factor.
Charging is an electrochemical reaction that needs heat.
Fast charging will not engage if the start temp is too low. Best start temperature is at least 85°F.
90F is better. Keep battery below 100F while charging, if it exceeds 101-102F it will disengage or stop charging entirely.
After reaching 70-75% or so it will ramp down.
At 90% it greatly ramps back protect the battery.
Try to limit charging to 30-90%; 40-72% being ideal for charge speed and battery longevity.
Avoid going below 20% as it greatly time. battery stress and provides little usable time.
Avoid charging of any kind if battery temp is below 72F as it can cause Li plating which permanently degrades the cell.

Drop in battery capacity and erratic fast charging can indicate a battery failure. This can happen at anytime but becomes more likely as the battery ages.
☠Any signs of cover bulging means the battery must be replaced asap. It rests on the display and can damage it, or worse...
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Guys why are you so obsessed with charging the phone super fast?

It is better to let it take it's time, it will let the battery stay healthy for longer. Realistically if you have all the fast charging options OFF, and left your phone to charge at night, this would be the best scenario. The device can easily last a full day anyway.