Preciso de carregar o telemóvel antes de sair de casa.

In European Portuguese, the verb precisar normally takes the preposition de before a noun or an infinitive.

So you get:

• Preciso de ajuda = I need help
• Preciso de sair = I need to leave
• Preciso de carregar o telemóvel = I need to charge the phone

If you leave out de, it sounds non-standard in Portugal. You may hear preciso carregar in some varieties of Brazilian Portuguese, but for Portugal, preciso de carregar is the safe and natural form.

Yes. Tenho de carregar o telemóvel is very natural in Portugal.

The difference is mainly one of nuance:

• Preciso de carregar... = I need to charge...
• Tenho de carregar... = I have to / must charge...

Preciso de often sounds like a practical need. Tenho de can sound a bit more like obligation or necessity.

In this sentence, both work well.

Good question. Carregar has several meanings, and context decides which one is intended.

With electronic devices, carregar usually means to charge:

• carregar o telemóvel = charge the phone
• carregar a bateria = charge the battery

In other contexts, carregar can also mean things like:

• to carry
• to load
• to press (for example, a button)

So here, because the object is o telemóvel, the meaning is clearly to charge.

In Portugal, telemóvel is the normal word for mobile phone / cell phone.

So:

• telemóvel = European Portuguese
• celular = much more common in Brazilian Portuguese

If you are learning Portuguese from Portugal, telemóvel is the word you should use.

Because in Portuguese, antes is followed by de when the next verb is in the infinitive.

So the pattern is:

• antes de + infinitive

Examples:

• antes de sair = before leaving
• antes de comer = before eating
• antes de dormir = before sleeping

So antes de sair de casa literally means before leaving home / before leaving the house.

After the preposition de in antes de, Portuguese normally uses the infinitive.

That is why you get:

• antes de sair
• not antes de saio
• not antes de saiu

It works a lot like English before leaving or before I leave, except Portuguese often prefers this preposition + infinitive structure.

Because Portuguese often drops subject pronouns when the verb ending already shows who the subject is.

Here:

• preciso = I need

So eu is not necessary.

You could say:

• Eu preciso de carregar o telemóvel

But that usually adds emphasis, contrast, or clarity. In normal speech, Preciso de carregar o telemóvel is completely natural.

In Portuguese, casa often behaves specially when it means home. In common expressions, it often appears without an article after a preposition:

• em casa = at home
• para casa = homeward / to home
• de casa = from home

So sair de casa usually means to leave home.

If you say da casa, that normally sounds more like from the house in a more specific, concrete sense, especially when you are thinking of a particular building rather than the idea of home.

Because Portuguese uses definite articles more often than English.

Here, o telemóvel means the phone, but in context it naturally means my phone or the phone I’m talking about.

Since the speaker clearly means a specific phone, the article is natural:

• carregar o telemóvel

If you said carregar um telemóvel, that would mean to charge a phone, any phone, not a specific one.

It can mean either, depending on context.

• leave home
• leave the house
• go out from home

In this sentence, the most natural English idea is probably before leaving home, but before leaving the house is also possible.

Portuguese casa often overlaps with the English idea of home, not just the physical building.

Preciso is the present indicative, first person singular, from precisar.

So literally it is I need.

Even though the charging will happen before a future action (before leaving home), Portuguese uses the present here because the need exists now:

• Preciso de carregar o telemóvel antes de sair de casa.
• I need to charge my phone before leaving home.

This is very normal in both Portuguese and English.

Yes, this is an interesting advanced point.

Portuguese has a personal infinitive, which can show the subject:

• antes de sair = before leaving
• antes de sairmos = before we leave
• antes de saíres = before you leave

In your sentence, sair is enough because the subject is already understood from preciso: the speaker is talking about their own action.

So antes de sair is the natural form here.