In lots of internet web pages it is possible to read statements as this one:

The less your phone is trying do while it's charging, the more quickly it will recharge. Airplane mode blocks any wireless radios on your device, reducing your phone's capabilities and therefore stopping it from doing so much.

However, from a point of view of electronics, it is intuitive imagine that when mobile is on and charging, both process draws current from charger "in parallel": from the point of view of the external power source, the load is smaller when on AND charging, it keeps its predefined voltage and provides more current.

It is true that internal battery loaders are nowadays very intelligent and can have dynamic adjustments. However, except if the manufacturer wants to reduce maximum power of the external charger, I do not see any technical reason that supports the hypotheses that load battery is faster when mobile is off or in low consumption modes.

Thus, my question is: which is the origin, from a circuit design point of view, of statements like the one said?


1 Answer 1


You do not properly understand how the battery is actually charged in your phone.

Although the device we use to charge a phone is called a charger, it is actually not a charger. It is a mains adapter or power supply. It's only task is to deliver a certain voltage, usually 5 Volt, to the phone. Depending on the model it can deliver up to 1 Ampere, 2 Ampere or even more at this 5 V.

It is the job of the phone to actually charge the battery. It has the circuit that is needed to charge the battery safely. It must be inside the phone so that it can monitor the battery voltage and temperature accurately.

Now regarding that statement:

This can be true of the power adapter cannot deliver enough current to keep the phone going (like when running a game) and at the same time charge the battery at full speed. For example, if the adapter can deliver only 1 A, the phone needs 0.5 A for running the game, there will be only 0.5 A left for charging the battery. If you'd stop gaming and leave the phone alone then that full 1 A is available for charging the battery so the phone would charge faster.

Another reason why a phone might charge more slowly when you're using it is that playing a game for example makes the phone hot. This makes the battery hot as well. The type of batteries that are used in phones must be charged more slowly when they are warm so as a safety measure the charging will be slowed down (by the charging circuit in the phone) in this case.

The statement suggests using airplane mode but that is nonsense, the wireless connections do not use that much power that you would notice the difference. If the wireless connections were using so much power then that phone would have a terrible battery life as normally these wireless connections are there to be used.

Some phone chargers are indeed "intelligent" but don't think too much of that. There are standards like Qualcomm Quick Charge which only works when the phone supports it. If it does, the phone will request a higher voltage from the charger allowing it to receive more power so the battery can be charger more quickly. Still, this faster charging will not happen when the battery is hot.

Do note that charging a battery quickly usually has an impact on the battery's lifetime. Charging it quickly places stress on the battery so it will wear out quicker. Slow charging is much friendlier to the battery.

  • \$\begingroup\$ Thanks for your answer. You point to two possible scenarios: the phone adapts to an external power source with a low power limit; and temperature. The first one seems unlikely, because the phone should know the max power of the current external power source and because it easy produce power units with 1A (5W at 5v) more of power. About second, most of the cited web pages talks about the scenarios of phone off or idle, being the clever idea change to idle in low profile modes. As you say, difference in temperature between idle and idle in low consumption profiles is small. \$\endgroup\$ Sep 25, 2017 at 8:29
  • \$\begingroup\$ the phone should know the max power of the current external power source No, it does not always know that. There are some protocols to inform the phone how much current it can draw but these protocols are not standardized between manufacturers. If a phone cannot identify the adapter properly it must play safe and only draw 0.5A which is what almost any USB port can deliver. (Officially that current should even be as low as 0.1A according to the official USB standard but since it would take ages to charge a phone with that and most ports can deliver 0.5A, 0.5A is used). \$\endgroup\$ Sep 25, 2017 at 8:59
  • \$\begingroup\$ You said " If you'd stop gaming and leave the phone alone then that full 1 A is available for charging the battery so the phone would charge faster.". Could you describe the circuit that allows send to phone device the current it needs and send ONLY the remainder current to the battery? Thanks. \$\endgroup\$ Sep 25, 2017 at 9:09
  • \$\begingroup\$ It is not done in a circuit but through the power management processor. That processor "knows" how much is available from the adapter, subtracts what is needed by the phone and orders the battery charger circuit to charge the battery at a certain current. \$\endgroup\$ Sep 25, 2017 at 9:11

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