Onde posso descartar a pilha?

Because onde means where, and in Portuguese it often comes at the beginning of a direct question, just like in English.

• Onde posso descartar a pilha? = Where can I dispose of the battery?

This is the most natural neutral word order. You could also say:

• Onde eu posso descartar a pilha?

That version is also correct, just a little more explicit because it includes eu.

Posso is the first-person singular form of the verb poder (to be able to / can) in the present tense.

So:

• eu posso = I can

In this sentence:

• Onde posso descartar a pilha? literally means
• Where can I dispose of the battery?

Portuguese often drops the subject pronoun when it is clear from the verb form, so posso already tells you the subject is I.

In Portuguese, subject pronouns are often omitted because the verb ending already shows who the subject is.

So both of these are correct:

• Onde posso descartar a pilha?
• Onde eu posso descartar a pilha?

The version without eu is very normal and natural. Adding eu can give a bit more emphasis or simply make the sentence slightly more explicit.

Because after poder (can / to be able to), Portuguese normally uses another verb in the infinitive.

So the structure is:

• posso + infinitive

Examples:

• posso descartar = I can dispose of
• posso fazer = I can do
• posso ir = I can go

This is similar to English can + base verb.

Descartar means something like to dispose of, discard, or get rid of, often in a more appropriate or responsible way.

For a battery, descartar is a very good choice because batteries usually need special disposal, not ordinary trash disposal.

Compare:

• descartar a pilha = dispose of the battery
• jogar fora a pilha = throw the battery away

For batteries, jogar fora can sound careless, because batteries should usually be taken to a proper collection point. So descartar is the better word here.

Portuguese uses definite articles much more often than English does.

So a pilha literally means the battery, but in context it can still translate naturally as the battery or simply a battery, depending on the situation.

In many real-life Portuguese sentences, the article sounds more natural than leaving it out.

• descartar a pilha sounds natural
• descartar pilha is less neutral and may sound more general or less complete

Not always. Pilha can also mean pile / stack, depending on context.

But in this sentence, because of descartar, the meaning is clearly battery.

A useful note for Brazilian Portuguese:

• pilha is often used for smaller household batteries, like AA or AAA batteries
• bateria is often used for larger batteries, like a car battery, phone battery, or rechargeable battery pack

So in context, a pilha probably means a regular disposable battery.

You would usually make both the article and the noun plural:

• Onde posso descartar as pilhas?
  = Where can I dispose of the batteries?

If you mean just one battery, use:

• a pilha

If you mean several:

• as pilhas

Yes, it is natural and correct, especially in a neutral or slightly careful style.

Other natural possibilities include:

• Onde eu posso descartar esta pilha?
  = Where can I dispose of this battery?

• Onde fica o ponto de descarte de pilhas?
  = Where is the battery disposal point?

• Onde posso jogar esta pilha fora?
  = Where can I throw this battery away?

The last one is more colloquial, but descartar is better if you want to sound appropriate and environmentally aware.

It is neutral. It works well in most situations.

It is not overly formal, but it is also not slangy. That makes it a very useful everyday sentence, especially when asking in a store, pharmacy, supermarket, condominium office, or public service location.

If you want to sound a little more polite, you could add:

• Por favor, onde posso descartar a pilha?
• Você sabe onde posso descartar a pilha?

In Brazilian Portuguese, pilha is pronounced roughly like PEEL-ya.

Important detail:

• lh in Portuguese is a special sound, similar to the lli in some pronunciations of million, or a ly sound for English speakers

So:

• pi ≈ pee
• lha ≈ lya

A rough English-friendly approximation is:

• PEEL-ya

A rough Brazilian Portuguese approximation would be:

ON-jeh POS-soh dehs-kar-TAR ah PEEL-ya?

A few notes:

• Onde: the d can sound a bit like j in many Brazilian accents, so ON-jee / ON-jeh is a useful approximation
• posso: stress on the first syllable
• descartar: stress on the last syllable, -tar
• a: usually a short unstressed ah
• pilha: PEEL-ya

Grammatically, yes, but it is much less natural here.

• Em que lugar posso descartar a pilha?

This is understandable, but most native speakers would simply say:

• Onde posso descartar a pilha?

So for normal conversation, onde is the best choice.