Can a phone battery give power to another device?

[Rumokiga]

Hi,

Hi I'm a real noob when it comes to electronics, I hope you can help me

So my question is, can a phone battery (more specifically a smartphone's) give power to a device that is asking for like 9 V, 4.2 Ah?

(sorry if I did post this thread in the wrong section, I went with the general forum to be safe )

 

[Audioguru]

A lithium battery in a smartphone is about 3.2V when it needs to be disconnected and charged and is 4.2V when it is fully charged. Then its average voltage is 3.7V. It can supply a very high current for a short duration but its capacity is about 2800mAh for a Galaxy S5 phone (all the batteries are different).

A Lithium battery must have a circuit to disconnect its load when its voltage has discharged to about 3.2V. Some batteries have a "protection circuit" inside that will do it.
If you want 9V then you must use a voltage stepup circuit. You asked for 4.2Ah which is a capacity, not a current. If you use a Lithium battery that averages 3.7V at a capacity of 2.8A then when you stepup its voltage to 9V then its capacity decreases to about 1.15Ah. Then the 9V will last for about 1.15 hours at a current of 1A.