Encendemos la radio a pilas.

Encendemos is the 1st person plural present indicative of encender.

• encender = to turn on / to switch on / to light
• encendemos = we turn on / we switch on

So the ending -emos tells you the subject is we.

Yes. In Spanish, the simple present can cover several ideas depending on context, such as:

• a habitual action: we turn on
• something happening now: we are turning on
• a near-future action: we’re turning on

If you want to make the right now idea extra clear, Spanish can also use:

• Estamos encendiendo la radio a pilas.

But the simple present is very common and natural.

Spanish often leaves out subject pronouns because the verb ending already shows who is doing the action.

• Encendemos already means we turn on
• Nosotros encendemos is also correct, but it adds emphasis or contrast

For example:

• Nosotros encendemos la radio, no ellos.
  = We turn on the radio, not them.

So in a normal sentence, leaving out nosotros is completely natural.

Spanish usually uses an article where English sometimes would not.

Here, la radio means the radio. It refers to a specific radio, or at least one that is understood from the context.

Spanish is much less likely than English to drop the article before a noun like this.

Because radio meaning radio set is normally feminine in Spanish:

• la radio
• una radio

So you say:

• Encendemos la radio.

Be careful: radio can also have other meanings in Spanish, and some of those can be masculine in other contexts, but for the everyday meaning of radio as the device, la radio is the normal form.

A pilas means that the radio runs on batteries or is battery-powered.

It describes the type of radio: not one plugged into the wall, but one that works using batteries.

So la radio a pilas is basically:

• the battery-powered radio
• the radio that runs on batteries

In Spanish, a can be used in expressions that describe how something works or what powers it.

So:

• radio a pilas = radio powered by batteries

This use is idiomatic. You learn it as a set expression, much like English says battery-powered rather than building it word-for-word.

Because the usual expression is a pilas, in the plural.

A pila is a battery/cell, and devices often use more than one, but even beyond that, a pilas is simply the normal fixed phrase for battery-powered.

So learners should usually remember:

• a pilas = battery-powered

rather than trying to translate it word by word every time.

Yes. Here a pilas describes la radio, not encendemos.

So the structure is:

• Encendemos = the action
• la radio a pilas = the thing being turned on

In other words, it means:

• We turn on the battery-powered radio

not

• We turn on the radio by means of batteries

Even though English might phrase it differently, in Spanish this is a normal way to attach that description to the noun.

Usually, a pilas is the most natural way here if you mean battery-powered.

• radio a pilas = a radio that runs on batteries

Con pilas would sound more literal, like with batteries, and it does not work as naturally as a label for the type of device.

So for this sentence, a pilas is the better choice.

Yes, it sounds natural in Spanish from Spain.

In Spain, pila is a very common word for an everyday battery, especially the kind used in small devices. So radio a pilas is a normal expression.

Depending on context, native speakers might also say something longer, such as:

• Encendemos la radio que va a pilas.

But Encendemos la radio a pilas is perfectly understandable and natural.