USB charging at different voltage question

[John Eucist]

I have an external battery charger for my Samsung Galaxy Note 4 removable batteries.  Using a USB voltage/current monitoring device I was alternating between two USB power sources to check any difference in the levels.  One USB power source charges at 4.85 volts at 0.46 amps while the other one charges at 5.16 volts at 0.46 amps.

Questions:
1) Is one of the chargers (probably the higher voltage one) "wrong" and bad for the batteries being charged?
2) Will the higher voltage one charge the pack faster at the same amperage?
 

[esaj]

1 hour ago, John Eucist said:

I have an external battery charger for my Samsung Galaxy Note 4 removable batteries.  Using a USB voltage/current monitoring device I was alternating between two USB power sources to check any difference in the levels.  One USB power source charges at 4.85 volts at 0.46 amps while the other one charges at 5.16 volts at 0.46 amps.

Questions:
1) Is one of the chargers (probably the higher voltage one) "wrong" and bad for the batteries being charged?
2) Will the higher voltage one charge the pack faster at the same amperage?
 

Uneducated guesses (as usual), but I think:

1) If it can overcharge (too high voltage) the batteries, yes, then it's bad for the cells

2) At the same amperage, no. It is the current that charges the batteries, the battery voltage goes up the more full charged it is. However, if the voltage is kept constant, the current is determined by the difference of voltages between the battery and the charger (as resistance stays pretty much constant), so the bigger the difference, the larger the current charging the packs and the faster it charges. As the battery voltage goes up during charging, the current drops as the difference drops.

U = RI  <=>  I = U/R  <=>  R = U/I

That's the Ohm's law, the voltage (U, sometimes marked as V), resistance (R) and current (I) are all interrelated. Change one, and it will affect one or both of the two others. The constant current-phase of the wheel chargers works by keeping the "out coming" voltage of the charger a certain amount above the battery voltage, so that I (the current) stays constant (and as R is constant, only the U can change). Technically, the R can (slightly) change as the temperature changes, but that's the general principle.

I should probably sometime take the time to open one of my chargers to check more closely how it does the voltage limiting (probably a mosfet or such which dissipates the "extra" voltage as heat?)

[John Eucist]

For some reason the "higher voltage" charger eventually came back down to 4.85 volts (after a while).  After that it did the usual (as you described) voltage slowly goes up and when near "full" the amperage drops until zero when it stops charging.

[MetricUSA]

Interestingly enough, there are no 5 volt batteries, you got 6 volt but only used in lights... And you got lithium at 3.6-4.2 volts, what we call a charger maybe only a power supply, the real charger I believe is built into the devices... So the inputs I don't think matter that much because the battery is only getting charged to 4.2 before stopping...some device can take on direct solar panel charge from anything from 5.5-7 volts, others reject it outright...

Then the 4.2 v lithium batteries have a booster board to take it back up to 5 volts again... maybe we should skip the bloody 5volt thing altogether...