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This is my second time changing my mobile because I forgot it all the night on the charger. I know there is an IC or circuit inside my phone that will disconnect the charger once the battery is fully charged,

So I brought my Multimeter and put my Lumia 520 under testing for 1 hour to see if there is anything I can build my charger on, and calculated everything; time, temperature of my mobile and my room, voltages and Amps. and this is the result enter image description here enter image description here In the beginning I was disappointed, I thought the voltage of my charger would drop down when my phone was closer to full charge. It took two minutes to charge my mobile only 1% and there was no change in temperature (just 3 celsius from 61% to 100%). But after full charge the temperature increased from 20 to 25, in twelve minutes.

I found something interesting when my battery is fully charged after 100%, the voltage changed from 5.39V to 5.50. My voltmeter is not that sensitive and I am sure its 4.50V. Anyway that little change will make a big difference.

I connected my charger to Arduino and made it stop the charger when the battery is full.

Some people said it's not necessary to do that, others say that heat will not have any effect on my battery or on my mobile!

From what I know the IC in the phone can't stop the charger completely, So that will damage the battery after extended use!

In the same time IC will be over heated if you let it do its job for a long time!

I am completely confused, I read some research about Lithium battery there is no recommended "specific point" to keep you battery on, or charging it at specific point, some research said 35, other 45, and the weirdest one was 80!

Can someone tell me if i am wrong or explain this to me!

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    \$\begingroup\$ recommended reading: BU-409: Charging Lithium-ion \$\endgroup\$ – Nick Alexeev May 25 '15 at 23:32
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    \$\begingroup\$ "This is my second time I change my mobile because I forget it all the night on charger." - what? are you saying you broke your mobile phone by leaving it plugged in, and had to get a new one? \$\endgroup\$ – user253751 May 26 '15 at 3:47
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    \$\begingroup\$ Perhaps the problem was with the charger rather than the phone. Some variation in the battery voltage is expected after fully charging because the charging circuit just tries to maintain it above a certain level rather than keep it fully charged all the time. In the last part, what is the "specific point" you refer to? Temperature? \$\endgroup\$ – Dr Coconut May 26 '15 at 10:28
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    \$\begingroup\$ What's the difference between "V" and "Charger V"? Where are they being measured? \$\endgroup\$ – pjc50 May 26 '15 at 12:22
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    \$\begingroup\$ We need to know where you are measuring the voltage. It's quite possible the charger supplies power to a circuit inside the phone all the time, even when fully charged. The charge controller is then responsible for how much of this gets to the battery. \$\endgroup\$ – David May 26 '15 at 12:23
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"I know there is an IC or circuit inside my phone that will disconnect the charger once the battery is fully charged"

Yes. Which is why you're not getting the results you expect.

Before USB, some chargers were directly connected to the battery and the phone lacked intelligent battery management. You would see voltages in the 3-4.2V range.

After USB, the "charger" is just a power supply and will always supply 5V. Charge control and end-of-charge should be managed by an IC inside the phone. It should theoretically be safe to leave it plugged in forever.

Overheating is bad for electronics, but they should not be overheating in normal operation. However, your charger is 5.5V rather than 5V, and this may be causing the problem. Counterfiet chargers can have the wrong voltage.

Reccomendations about what level of charge to keep batteries at are for long term storage (about 50% or slightly lower). Life may be improved by not charging beyond 80%. But, and this is very important, the state of charge displayed on the phone may not be accurate and may already account for this.

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  • \$\begingroup\$ Last thing, Is that true IC can fail for no reason ?! \$\endgroup\$ – narzan May 26 '15 at 13:22
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    \$\begingroup\$ No reason? Should be very rare. But if it's overheating (and it may be much hotter inside the case) then that can cause failure. \$\endgroup\$ – pjc50 May 26 '15 at 13:26
  • \$\begingroup\$ I used original charger, I think the multimeter not very sensitive or the battery of the multimeter is too low to read it 5.5V , so IC can fail, thanks allot Mr.pjc50 , your answer short and awesome :) \$\endgroup\$ – narzan May 26 '15 at 13:31

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