Do you have an extra battery?

还有备用的吗？

You need an extra battery pack.

需要备用电池。

A headlamp or flashlight, and extra batteries.

头灯或手电筒，以及备用电池。

So, here the word " spare" really means " spare battery, " an extra battery.

所以，这里的“备用”一词的真正意思是“备用电池”，即额外的电池。

We still need extra batteries for the flashlight.

我们还需要额外的手电筒电池。

They sell these little extra battery packs that are easy to pop in and out.

他们出售这些易于插入和取出的小型额外电池组。

Of course. I always bring an extra one, just in case. But I also have extra batteries if you want those instead.

当然，我总是多带一个，以防万一。但我还有多余的电池，如果你想要的话。

In 2017, Wang purchased his first agricultural drone, along with a generator, extra batteries, and insurance, at a cost of over 10,000 yuan ($1,377).

2017 年，王购买了他的第一架农业无人机，以及一个发电机、额外电池和保险，总费用超过 1 万元（1377 美元）。

So whenever you go, you'll want to bring waterproof hiking boots, a waterproof rain jacket, a swimsuit, flip flops, thin gloves, hiking socks, sunglasses, and a camera, with extra batteries.

所以无论何时，你都要带上防水的登山鞋、防水的雨衣、夹克、泳衣、人字拖、薄手套、登山袜、墨镜和相机，以及备用电池。