External battery

[VMuser]

Can someone pls explain why if I connect an external battery to my phone, it can only be used to recharge the internal battery?
Why can't these batteries not effectively increase the size of the battery connected to the phone?
In other words, if my phone has an internal battery of 1900 mah, and I connect a case with a battery of 2500 mah.... Why can't I have 4400 mah available?

Thx

 

[glc]

The battery in your phone is a 4.2 Volt battery.
The USB port is 5 Volt.
The external battery is 4.2 Volt.

When you connecet your external battery to the USB port, the following happens:
The external battery is boosted to 5V to the USB port.
The USB port on the phone uses the 5V to charge your internal 4.2V battery.
Both the external battery Voltage conversion and the charging of the phone battery
are not 100% efficient. You lose some capacity in the conversions.

 

[VMuser]

Thank you for the info glc