そうなんです、電池が減ることを英語では「死んでしまう」と表現するのです。
英語を勉強し始めたころの私が初めてこの表現を聞いたときにあまりにも意外な表現の仕方でびっくりした記憶があります。
My battery died.
電池が切れました。
My battery is dying. I need to charge soon.
電池切れになりそうです。すぐに充電しないと。
You can refer to your computer or you can just say 'this battery dies so fast'. Either way is fine to describe the short battery life.
-My computer's battery dies so fast.
My computer's battery' とパソコンに言及してもいいですし、単に 'This battery dies so fast'（このバッテリーは持ちが悪い）と言うこともできます。どちらでも、バッテリーの持ちの悪さを表現できます。
-My computer's battery dies so fast.
（パソコンのバッテリーの持ちが悪いです）
"losing its charge" "dying" and "getting low" are all ways of expressing that a battery is draining or losing its power. The adverb "really,"followed by an appropriate adjective, is a good way of emphasizing the speed at which the battery reaches 0%. And don't forget to define which or whose battery is being referred to.
E.g. My battery is at 3%. It dies really quick!
The computer's battery is getting low. I need to recharge it.
"losing its charge" と "dying" "getting low" これらは全て、バッテリーの残量が少ないことを表す言い方です。
形容詞の前に副詞 "really" を置くと、バッテリーの消耗の早さを強調できます。
また、どの、あるいは誰のバッテリーについて言っているのか明示することも忘れないでください。
【例】
My battery is at 3%. It dies really quick!（バッテリーが3％しかない。本当になくなるのが早い）
The computer's battery is getting low. I need to recharge it.（パソコンのバッテリーが減ってきているから、充電しないと）
The two sentences you see provided above are excellent ways to express to your listener that your computer's battery dies fast. In the second sentence you will see the term run out. This means to no longer have something in particular. This term is appropriate for informal settings, like talking with close friends or family. It would make a great addition to your vocabulary.
If you were talking about your computer's battery and you wanted to explain that the battery that it has dies fast, you could say any of the following: "My computer's battery dies fast", "This battery on my computer dies very quickly" or "This battery inside my computer drains fast". All three of these sentences adequately explain what you are trying to communicate.
パソコンのバッテリーの持ちが悪いことは、次のように説明できます。
"My computer's battery dies fast"
"This battery on my computer dies very quickly"
"This battery inside my computer drains fast"
（パソコンのバッテリーの持ちが悪いです）
これらどの文でも、あなたの言いたいことが伝わります。
When talking about your computer's battery and you want to explain that the battery dies fast, then any of the above exampled statements is quite adequate.
To run down/out - to deplete/empty
To be knackered - to be exhausted or useless or defunct (slang)
To be on one's way out - to be at the point of retirement or approaching the end of life.
パソコンのバッテリーの持ちが悪いことを説明したいなら、上記の文どれも使うことができます。
To run down/out - 使い果たす/空になる
To be knackered -【スラング】使い尽くされた/使いものにならない/機能しなくなった
To be on one's way out - 間もなく退職する/寿命が近づいている
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