iPhoneの電池がすぐに切れるようになっちゃったって英語でなんて言うの？

"My iPhone battery goes from 100% to 1% very quickly." 100% is when your battery is fully charged but it goes down to 1% meaning you cannot use it.. You could also say, "My iPhone battery is not holding a charge for very long." (Holding a charge - keeping the battery at full power) "The battery on my iPhone drains quickly." Drains - to run out fast and needs to be charged again. "My iPhone battery has been dying rapidly." Dying - Draining, or losing its charge. Quickly - very fast, in a short amount of time.

Something which is duff is useless or broken Eg. 'John spent a thousand pounds on a duff car which broke down the first day he had it.'

This is a way to talk about the fact that your battery is not as good as it was when your originally bought the phone. Plus, in the second sentence, it talks about what is wrong with it. I hope that this helps :)

As we know, over time a phone's battery will slowly run out of battery quicker because the battery is slowly dying. If we have had a phone for a few years and the battery is always dying quickly, we could say some things like: 1) My iPhone's battery doesn't last very long anymore. 2) My iPhone runs out of battery really fast now.

Sluggish is a word used to describe something that is slow and doesn't work very well which causes it to not move very fast. It is derived from the word 'slug' which is a creature similar to a snail, without a shell.

You can explain that your battery runs out very fast by saying: "My iPhone battery drains very quickly." "My iPhone battery dies very quickly." "drains" and "dies" in this scenario refers to the iPhone battery running out of charge at a fast rate.