I've been running some tests on USB charges from different manufacturers checking voltagem and current.

I noticed that some usb charges do deliver 4.9 to 5.2 volts and from 500mA to 2.4A.

My manufacturer's charger (Apple) delivers 1000mA @ 5.05v to my phone.

My questions are:

  • If I use a 600mA @ 4.96v could reduce my battery life?
  • if I use a 5v at less current (slow charge) will it prolongue the battery life?


  • \$\begingroup\$ Reduce and prolong in comparison to what? If you are worried about the life of your device you might be over thinking it. \$\endgroup\$ – Wesley Lee May 12 '17 at 14:46
  • 3
    \$\begingroup\$ The fundamental oversight here is that the charge rate is controlled by the charging circuit inside the phone, not the external power supply. All that does is determine a maximum (either specifically in the form of an current/voltage curve) that it is willing to supply. But the USB-sourced charge circuit inside the phone won't use more of that capability than it is designed to. Conceivably there could be an "end user hack" in using a lower capability power source to try to charge the battery extra-slowly, but that's in the realm of second guessing the manufacturer. \$\endgroup\$ – Chris Stratton May 12 '17 at 15:00

Generally battery life is increased with reduced stress, and stress for a battery is current (among others). Reduce the current (both discharge and charge) and you increase your battery life.

Chris Stratton points out very well that the main limitation you face is that the charge circuit inside is controlling the charge current to the battery.

So the voltage is basically irrelevant. It needs to be stepped down in any case (4.35 V maximum cell voltage for all lithium based chemistries I know of, most are 4.2 V).

Now with the current capacity of your wall adapter you can have some influence. Usually the device has to negotiate how much power it needs if it needs more than 100 mA. Well most of the devices simply take 500 mA. Above that it should have some sort of protocol or charger detection.

So you can reduce the charging rate if you select a slow charge mechanism either in your phone or with a 500 mA max rated charger, so the phone has to use the slow charge mechanism. With this you'll end up with a reasonably small charge current (in the order of 1/2 C).

Most benefit to battery life would be a reduced end of charging voltage like 4 V instead of 4.2 V, but as this reduces the run time of products significantly, probably no manufacturer employs this for a phone. You'd have to unplug it at 80% charge or something to get this benefit.

  • \$\begingroup\$ Thanks a lot for your reply !!! Did answered my question... \$\endgroup\$ – Rafael Dalben May 26 '17 at 19:55

Batteries can handle watts of charge discharge based on some C value rating.

This is according to their thermal resistance to losses and resulting temp rise. Thus a large flat pack can run cooler than a cyl pack if they both have the same 5~35 mOhm ESR when new. ESR rises sharply below 10% SoC and slowly with aging until dead.

You cannot compare Apples and Oranges with current. It depends on battery C charge rate for a given string voltage and P=V*I and heat loss is Pd=I^ ESR.

Prolonged life is controlled by Arhennius effect and temperature rise of electrodes inside. Longest life is <10'C inside or a few degrees outside as this Law is roughly 1/2 life for each 10'C - 12'C rise.

But battery life curves are rated in cycles and C/20 and other rates for comparison.

But you can sense temperature and correlate that with aging.

The other thing is batteries actually get lower ESR and can deliver more current when hot, while aging faster.

This is just a brief answer. go to battery university site for future info.


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