I did a charge on this page and could not find the answer I was looking for. Perhaps it was over my head, or perhaps I was using the wrong search terms, so here goes nothing:
I am trying to understand something about the battery pack I've purchased and the number of times it can charge my electronic gadgets. I purchased a RAVPower 15000mAh battery pack, which can be found here:
On the back of the battery pack it says the following:
Capacity: 15000mAh/55.5Wh Input: DC5V/1.5A Output: DC5V/4.5A Total
ON the amazon page it says it can charge an iPhone 6 6.2 times.
My understanding is that an iPhone 6 battery has the following specs:
3.82V 6.91Wh 1809mAh (1000*6.91Wh/3.82V)
When taking the capacity of 15000mAh I figured that I could get to the number of Wh by just multiplying by the 5V, but it appears that the actual battery cells are 3.7V cells, so the 15000*3.7/1000 = 55.5Wh, which makes sense to me, but...
When I take the 55.5Wh capacity and I divide by the capacity of the 6.91Wh iPhone I get to 8 charges, which differs from the company claim of 6.2 charges.
So here is where I am confused.
I can get to the 6.2 charges by taking the 3.82V/5V and multiplying by the battery capacity of 55.5Wh and then dividing the result by the 6.91Wh capacity of the iPhone battery.
It seems as if I've already stepped down the Wh capacity of the battery by multiplying by 3.7V above, yet I'm stepping down the battery capacity again. Or am I really just losing the remaining charges because the output is 5V, but it gets stepped down to 3.82V when it hits the iPhone and the rest is lost due to inefficiency? Or is there some other explanation?
Also, now if I take this battery pack and I want to charge it using the RAVPower 9W solar panel:
This panel tells me that it is a 5V panel capable of producing 1.8A of output. I see that my max input for the battery is 5V at 1.5A, so I believe that I should be able to add 7.5W of battery capacity per hour under full sunlight. My experience has been closer to about 5W of battery capacity per hour, which brings me in the ballpark of my other calculations where I'm actually charging the battery pack at 3.7V*1.5A = ~5.5W.
And what does the 5V on the input and output actually mean? Is the battery voltage stepped up to make sure that I charge any gadget that is less than 5V? Or is there some other reason?
Thank you in advance for your help!