FP2 not charging when battery warm

Whenever my phone gets warm/hot (not overheated, just warm the way it gets in normal use) it refuses to charge. When I plug in the cable the lightning icon appears on the battery icon, but the phone doesn’t charge. The charging light doesn’t light up, and when I go to ‘battery’ in the settings, it says “not charging”. If I take the battery out and put it somewhere cool to cool down for a while it’ll charge again after I put it back in and turn on the phone. The phone can still be warm from the use, so it has definitely to do with the battery temperature, not the phone temperature itself, though it’s probably the phone that warms up the battery as well (the batteries don’t get hot, merely even warm). I also have two batteries (both FPs’ own) so when one of them refuses to get charged I can swap to the other, which will charge normally. When this battery then refuses to charge later on when it gets warm I can just swap back to the first one, which will then charge again.
I don’t see any signs of bloating or other injuries on the batteries.

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Iirc the threshold for stopping the charge process is somewhere at ~42°C as @Dr_Cool once stated after having investigated and performed tests with the app “Automate”.


Yes I can confirm it. Charging adds heat to the battery, the intention then is to protect it against overheating.

Best thing to do is to stop using the phone when it happens, and put the phone in a cooler place. It overheats much more frequently for example when I use it under the sun.


Strange thing with my FP2 is, that charging leads to overheating, when the phone is turned off.
Especially when the battery is drained and the phone shut itself off.
Once I plug it in, it is charging up to 5% before it starts acting like a table-top grill.
As soon as I turn on the phone it is cooling down and resumes charging.

And I almost never use the phone when it’s charging.

Maybe because it wants to be a table top grill…:grin:

No, seriously…that’s logical from the electrical pov.
Well, not really overheating as you call it, but heating up.
As when the phone has turning off itself due to the almost fully spent battery (3% level iirc) the batteries internal resistance is high.
So at the beginning of the charge at this state the current is internally limited. But also the charge controller is matched to a battery type specific charge curve. The charging starts with a lower current but is ramped up after having reached a certain charge level. This is when the heat exposure starts due to the current. It should decrease again the more it reaches the 100% level.
This can vary depending e.g. on wear of the battery but also proper contacting to reduce incorrect voltage and capacity determination and more.
Keep the phone on a solid surface and turned on its face if possible, to prevent heat accumulation.

Maybe that’s why the heat increase is not that high. But using the phone while it’s charged should accumulate some more heat.
Using a data cable and a computer to charge (charging over USB mode) will reduce the charge current and heat development, but increase the charge time.

@Dr_Cool could gather quite some experience in this issue whilst experiencing and programming with the “Automate” app to have his phone operating smooth in every possible state.

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Thank you for your answers! So after googling a bit, there seems to be nothing I can do about it, other than just give a pause for the phone to let it cool down. Well, it’s good to know it’s normal and there’s a good reason for it too. I just got a new FP2 for the first one being faulty, it would have sucked if there was something wrong with this one too.

I’m probably going to try some modifications for the back cover though, not just yet but after I’ve been able to buy an axtra back cover. I was thinking about trying to replace part of the cover with metal and see if it works. I saw there was some older threads about it already, but didn’t find any clear answers if it would work.

Thx for this general insight.

In my case the phone - when turned off - stops charging at 5%. At that point it’s heating up only. I even - accidentally left it in that state for a few hours; still just 5%.
Then I turn it on and it continues charging and cooling down.

Maybe the current of my chargers is to high for the drained battery and just the small energy consumption of the phone’s antenna (background app activity should be switched off) makes the difference.
I just wonder everytime.

Thank you for the valuable hints - my phone has the same behaviour but I never traced it back to the battery temperature, for me simply taking out the battery seemed to be the solution.

But there is a big problem with that for me - this behaviour most often shows when I am navigating in my car. And then I simply have to use the phone and charge it in parallel, so I have no chance to let the battery cool down. This got me stranded on the motorway twice already. All my previous phones never showed such a behaviour. I would be very grateful for a solution.

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Other phones may vary on how they deal with the problem, but in the end the physics is always the same: or the phone needs to slow down hardware use, or charging must be restricted, or the battery must get damaged faster than necessary.

You may want to think about ways to reduce data and CPU use on the run and how to turn off unnecessary features and apps. I know that my Fairphone runs longer and cooler compared to my previous phones because with the Open OS I can block all wasteful activities from GAFAs.

You may try to find a car charger with lower current delivery. It will charge the phone less fast but reduce overheating.

Finally, maybe you can position your phone in front of a vent, or consider one of the many different kinds of cooling gadgets for electronic devices.


A metal case can help with heat dissipation but maybe not much better than the current plastic case, It can also interfere with radio and GPS signals, so I’m a bit sceptical concerning this approach.


It might also help to have it fully charged when starting navigation. When it’s nearly fully charged the charging current goes down and it heats less.


Correct answer as I would point out. But there are other option too.

All this could help in your situation.


What makes me wonder…you write:

How do you know?
Is it an estimation of the charge level compared to the blue fill level of the battery?

Or do you mean:

Like just the display switched off?

Actually no chargers current can (ever) be too high as it is depending on / adjusted with the devices demand.
It’s the voltage that needs to be correct as it can kill your device otherwise.
Limiting the current by using a weak charger (as DR_Cool has stated) is a simple way for anyone to have limited influence on it in such a situation like too much heat development.
But you cannot grill your device with too much current, but too high voltage.
Too less current will result is extended charge times, lower heat development or possibly no charging at all.

Have you tried to calibrate your battery?

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It’s the value given with the blue fill level, not just an estimation unless you mean estimation by the software.

  1. The battery has actually run dry and the phone shut itself down.
  2. I plug in the charger
  3. Charging starts and after a while the phone turns hot. When checking the status, the phone always shows 5%. Checking again some time later, nothing has changed.
  4. I turn on the phone, unlocking the sim.
  5. Charging resumes and the temperature goes down.

I have not performed a battery calibration, as the performance - otherwise - seems quite fine. Usually the battery lasts me two to three days at least.

Thank you for this thread, I also observed this recently, before reading it (but after the last update, maybe it is linked, or I just didn’t observe before).

When my kids use my Fairphone to play very CPU consuming games, the battery both drains quickly, and heats a lot, and it becomes impossible to charge, which is a problem if I need the phone for myself… Knowing from here that it is linked to temperature, I just solves the problem by cooling down the phone quickly posing it one an ice block, it seems to help a lot.

Ice block might not be the best idea, for the phone could end up getting moisture inside. Idk, if you sealed the phone in a ziploc bag first though?

Sure, no direct contact with water. In fact, I think the correct word for what I used is ice pack or freeze pack, which i placed inside some fabric, anything to soften the cooling. With this method, within 5 minutes (10 maximum), charging starts back, and ice is not necessary any more.


Yes I remember. This feature initially was implemented in Lollipop but removed with some later update. Now re-implemented after some complaints.

Your batteries behavior indeed is unusual. I don’t see much difference when charging between being switched-off and running beside more current being needed to keep the full circuitry powered. So how come the temperature specifically goes down and charging continues then, is curious.
Do you have the chance to test another battery?
Are there strange signs (gaps…) visible in your battery gauge?

No, besides that behaviour everything is just fine.
Therefore I have no second battery and I can’t get hold of one for testing either.
I just don’t charge the phone when it’s off, but turn it on as soon as possible; so no worries for me; I just wanted to share my funny experience.

And it’s not likely to be something that might be related to an ageing or slowly dying battery, as I noticed this already many months ago, without any decrease in battery power since then.

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