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Charging speed seems slow than expected on Pixel 2

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By Charkatak, Senior Member on 9th June 2018, 11:08 PM
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Hi all! My Pixel 2 charges fast(~2700mA) up to first ~20%, then the current changes to 1370mA till almost to 90%, then slows a bit till the 100%. I have used Ampere to check the charging speed. I expected the phone to charge to at least 50% at a fast rate, then slow down a bit.
I recently acquired the device and it had May patch, but then after setting the device up, it prompted me for June patch and I installed it. Don't know if the new update could be the problem.
 
 
10th June 2018, 11:47 PM |#2  
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The phone will take battery temperature into account as well. Do you have a way to monitor that and correlate it with where the current switch points are?

Sent from my Pixel 2 using Tapatalk
11th June 2018, 03:41 AM |#3  
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Quote:
Originally Posted by DurhamHusker

The phone will take battery temperature into account as well. Do you have a way to monitor that and correlate it with where the current switch points are?

I charge my phone early in the morning where it was not used all night. No battery drain apps at all. It just charges from almost 0 to 20 percent really fast, but then slows to a steady 1370 mA.
11th June 2018, 04:01 AM |#4  
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What I mean is ... Try charging from a different start point.

By the time it's charged at 2.7 amps to go from 0 to 20 it might be getting warm. You might try charging when it's at 20 and cool and see what happens. Or stop at 20 and let it cool down before going any further and see what happens.

Sent from my Pixel 2 using Tapatalk
11th June 2018, 05:12 AM |#5  
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Quote:
Originally Posted by DurhamHusker

What I mean is ... Try charging from a different start point.

By the time it's charged at 2.7 amps to go from 0 to 20 it might be getting warm. You might try charging when it's at 20 and cool and see what happens. Or stop at 20 and let it cool down before going any further and see what happens.

Sent from my Pixel 2 using Tapatalk

Oh, I see now. Good point. Will try it!
11th June 2018, 06:22 PM |#6  
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Originally Posted by Charkatak

Oh, I see now. Good point. Will try it!

Quote:
Originally Posted by DurhamHusker

What I mean is ... Try charging from a different start point.

By the time it's charged at 2.7 amps to go from 0 to 20 it might be getting warm. You might try charging when it's at 20 and cool and see what happens. Or stop at 20 and let it cool down before going any further and see what happens.

Sent from my Pixel 2 using Tapatalk

So I did some testing and here is what I see:

Phone starts to charge at a good 2700mA rate for ~ a minute, then slows down to 1370mA. It doesn't really matter if phone has 5% of battery before I start charging or 20% or 40%, the charging pattern is the same. At start the battery temperature is ~32 C and when it charges at 2700 for that first minute or so, the temp rises to ~36 C, then phone drops the charging rate to 1370. Phone is pretty much room temperature and not hot or anything like that. I have 2 Google chargers; One is from original Pixel and the other is from Pixel 2 box. Both do the same thing and charge at the same rate.

There are no abnormal app activity or any battery drain. I am using Ampere app to check mA. Did anyone come across this?
11th June 2018, 06:47 PM |#7  
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It appears you've discovered the magic battery temperature cutoff that HTC has selected for the Pixel 2 ... and that seems to be around 35 or 36 degrees.

For every 10 C rise in temperature, battery degradation doubles by almost every measurable metric. It doesn't surprise me that at around 35 C your phone appears to limit the charge current ... seemingly to avoid making the battery any hotter. Taking the temperature higher for the charge cycle (or for any other reason) will degrade the battery over time. Deep discharges toward zero also reduce the life of a battery. (Keeping it at 50% or higher is recommended for lithium-ion rechargeable batteries.)

If you can cool the phone down to 25 C before starting to charge, I'd be willing to bet that it will charge at the higher rate for longer. Maybe put a small fan on the phone or set it in front of an A/C vent while it charges and see what happens then.
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11th June 2018, 07:28 PM |#8  
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Quote:
Originally Posted by DurhamHusker

It appears you've discovered the magic battery temperature cutoff that HTC has selected for the Pixel 2 ... and that seems to be around 35 or 36 degrees.

For every 10 C rise in temperature, battery degradation doubles by almost every measurable metric. It doesn't surprise me that at around 35 C your phone appears to limit the charge current ... seemingly to avoid making the battery any hotter. Taking the temperature higher for the charge cycle (or for any other reason) will degrade the battery over time. Deep discharges toward zero also reduce the life of a battery. (Keeping it at 50% or higher is recommended for lithium-ion rechargeable batteries.)

If you can cool the phone down to 25 C before starting to charge, I'd be willing to bet that it will charge at the higher rate for longer. Maybe put a small fan on the phone or set it in front of an A/C vent while it charges and see what happens then.

That is interesting as I have had different phones which got even warmer than Pixel 2, but still charged at a good rate. I do know that after 80% of charge of so, the charge rate does go down, which isn't a surprise to me. I just picked up my phone, after it was sitting idle for few hours and see that battery/phone temp is 25 C. I will make sure to start charging phone at a low temperature and see if it will keep the fast charge rate longer.

What you mentioned about the "keeping battery at 50% or so). Did you mean that when battery goes down to 50 or so %, charge it? I usually run battery until about 30 or so % before charging it.
11th June 2018, 08:58 PM |#9  
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Quote:
Originally Posted by Charkatak

That is interesting as I have had different phones which got even warmer than Pixel 2, but still charged at a good rate. I do know that after 80% of charge of so, the charge rate does go down, which isn't a surprise to me. I just picked up my phone, after it was sitting idle for few hours and see that battery/phone temp is 25 C. I will make sure to start charging phone at a low temperature and see if it will keep the fast charge rate longer.

What you mentioned about the "keeping battery at 50% or so). Did you mean that when battery goes down to 50 or so %, charge it? I usually run battery until about 30 or so % before charging it.

Yes, charging it when it gets to around 50%, based on a number of studies, seems to be the way to go.

Deep discharges and hot temperatures are enemies of battery life for today's lithium-ion cells.
12th June 2018, 05:21 AM |#10  
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Quote:
Originally Posted by DurhamHusker

Yes, charging it when it gets to around 50%, based on a number of studies, seems to be the way to go.

Deep discharges and hot temperatures are enemies of battery life for today's lithium-ion cells.

I have tried just now to start charging the phone when it is 23 C, but still get the same result. Could it be the June security patch?

Update: So the phone charged by rate of 1370mA from 22% to 100% in 1h 25m. So going from 0 to 100% should take ~1h 45m? Can anyone confirm how long it takes to charge Pixel 2 using original charger?
12th June 2018, 10:44 AM |#11  
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Quote:
Originally Posted by DurhamHusker

Yes, charging it when it gets to around 50%, based on a number of studies, seems to be the way to go.

Deep discharges and hot temperatures are enemies of battery life for today's lithium-ion cells.

Go a reference to these studies?

This app vendor has seen a lot and isn't convinced discharging to low values has much material effect on battery service life. Charging to high levels does, however. Interesting read I think... with commentry on the often quoted Battery University pages. I agree that heat isn't good whatever.
https://accubattery.zendesk.com/hc/e...nd-methodology
https://accubattery.zendesk.com/hc/e...ersity-article
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