Battery life is a critical aspect of mobile phones. I have a 4000mAh battery and I can use my phone without charging for even 2-3 days without internet.

But I have lost the charger that came with the phone, which is having a current rating of 2A. So I am concerned about the health of my battery when I plug it into another charger or my USB 3.0 port.

I know that if a load is connected to a source, the voltage ratings of both the load and the source should be the same and the current rating of the source should be greater than or equal to that of the load. The idea here being that the load will draw the amount of current that it needs. So I can safely connect a 3V LED to a 6A 3V source and it would work.

But upon research I found that this is not the case with charging of batteries. In this case current supplied is also an important parameter. But don't smartphones have internal circuits that regulate the current that goes into the battery?

How good a practice is it to charge my phone which had a 2A charger in the box using a USB 3.0(1.5A) or usb 2.0(500 mA)? How about using a .4A Samsung charger? Will this result in any damage in the long run?

  • \$\begingroup\$ If phone input is "USB" then any 5V USB charger will probably work OK. No danage to the phone will occur if current capability of charger is too low . | A VERY low capacity charger may stop charging at CC to CV transitiomn if I charger < I terminate for the phone. This wou;d give lpow charge capacity but usefully longer battery life. \$\endgroup\$ – Russell McMahon Oct 9 '15 at 13:33

As phones are charged via 5V from the USB (or "phone charger") but no battery chemistry is available with 5V - there has to be some circuit inside the phone to handle proper charging of the battery. So as far as this goes any 5V charger should be fine.

Your problem might be that your phone might try to use too much current from your available chargers. Normally the amount of current is negotiated over USB - but I actually don't know how this is done in the phones and chargers.

  • \$\begingroup\$ You mean that the phone could try to draw more current from my laptop. But according to USB 3.0 specification, the current is limited to 1.5A. So is the final verdict that it is perfectly safe? \$\endgroup\$ – daltonfury42 Oct 9 '15 at 12:13
  • \$\begingroup\$ On a laptop your USB port should be protected against overcurrent situations and switch off if the device connected is doing something out of specification. The device and laptop will negotiate on how much current is acceptable. Just with your standard wall plug chargers, I don't know how they work it out there, maybe it just takes all it can get before the voltage drops too low. \$\endgroup\$ – Arsenal Oct 9 '15 at 12:15
  • \$\begingroup\$ @daltonfury42 Yes, it is safe. The voltage must match, for anything USB this will be 5V (it can be higher but then charger and phone will decide about this together, so still 100% safe). The current the charger can deliver must be equal or higher than your phone takes, usually 1A or more is OK. So yes use a USB 3.0 socket to charge it is perfectly safe. \$\endgroup\$ – Bimpelrekkie Oct 9 '15 at 13:02
  • \$\begingroup\$ @Arsenal Qualcomm Quickcharge is a protocol for faster charging, the negotiation over USB is done with the phone applying certain voltages to the USB data lines. A chip in the charger recognizes this and then increases the USB voltage as requested by the phone. You need phone and charger to be Quickcharge compatible of course. Otherwise nothing happens. \$\endgroup\$ – Bimpelrekkie Oct 9 '15 at 13:07
  • \$\begingroup\$ @FakeMoustache thanks for explaining that, got me wondering a few times but not hard enough to make me research it. \$\endgroup\$ – Arsenal Oct 9 '15 at 13:10

It won't result in any damage for your battery. Speaking about batteries, the slower you charge them, the better it is. If you have a 500mA, it will take more time to charge the battery but won't damage it.

The only thing that could happen is if you have a charger with really little curent (usually a charger who broke itself alone I still don't understand why) the battery will not be fully charged at the end. Then you will have to charge it again more often which is not really nice for batteries. But with a 500mA charger it is OK to charge your battery.

  • \$\begingroup\$ Lithium batteries last longer if they are not fully charged - even though they have to be charged more often. (in terms of battery life, not device run time between charges of course) \$\endgroup\$ – Arsenal Oct 9 '15 at 12:11
  • \$\begingroup\$ I though it was still true on lithium battery, I know there is no more memory effect but I though charging it more often would damage them a little bit more quickly. \$\endgroup\$ – damien Oct 9 '15 at 12:16
  • \$\begingroup\$ if you cycle them between 20% and 80% charge you can increase the number of cycles by a large amount before the capacity drops to the same level as when using them 0% to 100%. If you charge them to 80% the end voltage will be lower, which will help as well. Have a read \$\endgroup\$ – Arsenal Oct 9 '15 at 12:19

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