I got a battery bank from China and it says in the back that the rated capacity is 20,000mAh (3.7V). After some use (charging my laptop) I decided to open the thing and I noticed four cells of 5000mAh connected in series at 14.8V. The battery bank offers two ports: 1 USB port of 5V,2A(max) and one DC output of 19V/4A(max). I contacted the people and they said that the configuration of 4x5000mAh in series (achieving 14.8V) is the same as the 20,000mAh at 3.7V (4x5000mAh in parallel), because the power is the same.
How can that be? are they flat out lying? shouldn't a parallel connection give you more capacity than the series connection? even if the power at any given instant is the same, the capacity should be 5000mAh and not 20,000mAh, wouldn't it? or is it that the DC-DC converter design requirements inside the product make the two configurations equivalent?
I think inside there is this configuration: 14.8V stepped down to 5V@2A and 14.8 stepped up to 19V@4A. Since stepping up from 3.7V to 19V and still give 4A(max) would ideally require more current from the 20,000mAh battery than from the 5000mAh battery (since the voltage step would be from 14.8 to 19, not so big), is it then that the two configurations (series and parallel) are similar/equal and the reason they are marketing their product as 20,000mAh?
I would really hope you guys could help me with this puzzle and point any mistakes I've made. Thanks in advance!