The watch's battery is worn down.
電池沒電了。
1 battery 電池
replace the battery
更換電池
The battery is flat.
電池沒電了。
a battery of..
一系列；一批；一大群
He faced a battery of questions.
他面臨一系列問題。
2 worn down 磨損不堪的；疲憊不堪的..
My heels of my shoes have worn down.
我的鞋跟磨損了。
worn out
疲憊的
After the race,he is worn out.
賽后，他疲憊不堪。

A:What can I do for you?
有什么可以幫您的？
B:Yes.There is something wrong with my watch.It stopped several hours ago.
是的。我的表壞了。幾個小時前它不走了。
A:Let me have a look.The watch's battery is worn down.
讓我看看。電池沒電了。
B:How much is a battery?
一個電池多少錢？
A:50 dollars.
50美元。
B:How long will it last?
能用多長時間？
A:About 2 years.
大約兩年。