# How many flash drives can you power with an iPhone battery?

I will give a very specific example: Hardware:

• Iphone X device with 2716 mAH capacity battery, 3.81V
• Iphone "dongle" lightning to USB 3.0 port, bus-powered
• USB hub 3.0, bus-powered, 3V, 200 mA, four-ports
• USB flash drives 3.0, 900 mA and 5V +- 10% operating voltage bus-powered

Circuit setting and analysis:

• Connect Iphone to dongle, to USB hub and plug in USB flash drives.For me, the circuit is in series for component 3 (Hub) and components 4 (the drives). The drives are in parallel inside their component.

• Hence the hub receives 3.81/2 = 1.905 V and the drives 1.905 V. The flash drives receive x/n mA where n is the number of drives plugged in and x the current in amps release by the IPhone battery. Here I have a missing variable: maximum discharge current of the iPhone X battery, which may of may not be limited by software.

• I have battery capacity at 2716mAH, and current requirements of 4*900mA = 3,600 mA so I can last up to 2716seconds on a full iPhone battery theoretically (if the battery had a 5V voltage).

Questions

1. Is the above analysis correct?
2. When an electrical device says 5V operating voltage, 900mA, does it have to be these precise conditions or can power the device with equivalent wattage i.e 1.905V and 2,362 mA?
3. Assuming maximum discharge current is 3,600 mA, how many USB flash drives as above can I bus power?

Edits

1. For 1.,it was commented that the circuit is in parallel, the USB hub is not in series.
2. For 2., a link was provided by brhans Choosing power supply, how to get the voltage and current ratings? to a similar question which advises to keep voltage within recommended tolerance band and current amperage too. Hence, as user towe commented, there will be a problem connecting 5V appliances to 3.8 V battery. Maybe some USB hubs can do this (ex:)
3. User Chris Patton has mentioned that connecting multiple flash drives to a phone is a bad idea. Why is that?
• 900 mA seems very excessive for a simple USB flash drive. Around 0.2 W or 40 mA seem to be more common.
– towe
Aug 10, 2020 at 8:27
• I have similar 2.0 drives with 200 mA. I just want to get the reasoning right. Aug 10, 2020 at 8:42
• Since you'll likely be limited by the 3.7V -> 5V internal step up, this might be relevant: apple.stackexchange.com/questions/119707/… The battery itself could probably handle quite a bit more.
– towe
Aug 10, 2020 at 9:39
• Nothing is in series. Even though the drives are connected through the hub, the +5V passes through the hub to the drives. Everything gets 5 volts. Aug 10, 2020 at 9:54
• Does this answer your question? Choosing power supply, how to get the voltage and current ratings? Aug 10, 2020 at 13:26