Is it okay if I use your cellphone?
1. I'm sorry, but it's broken.
2. I'm sorry, but it is out of battery. i need to charge it.
3. i'm sorry, but I can't use it at the moment. Where can I charge my cellphone.
4. i'm sorry, but it's not mine. I have to return it.
5. I'm sorry, but it doesn't have enough battery.
(Are the expressions all grammatical? Would you let me know some more expression which I can use in the situation?)
In #s 2 and 5, the word "battery" needs to be replaced by "power" -- the battery is still there, but its power has been used up. Also in #2, the second sentence needs to have "battery" in place of "it."
All others are fine.