Learn Hardcore Spanish (Spain): Se me acabó la batería, así que no pude responder a tu llamada. - My battery ran out, so I couldn’t answer your call.

It’s the so‑called accidental or dative “se.” Structure: se + indirect object pronoun (me/te/le...) + verb (3rd person) + subject. It conveys that something happened to you without your control: Se me acabó la batería = “The battery ran out on me.” The subject is the thing that ran out (here, la batería), not “me.”

Why is it acabó (3rd person singular) and not first person?

Because the subject is la batería (3rd person singular). The verb agrees with the subject:

Singular: Se me acabó la batería.
Plural: Se me acabaron las baterías.

Can I drop either se or me? For example: Se acabó la batería or Me acabó la batería?

Se acabó la batería is fine and means “The battery ran out,” but it doesn’t highlight that it affected you personally.
Me acabó la batería is incorrect here. You need the pronominal form acabarse to mean “run out,” so keep se. The me shows it affected “me.”

Why is it la batería and not mi batería?

Spanish often uses the definite article with body parts and personal belongings when the owner is clear from the indirect pronoun. Se me acabó la batería already implies it’s your battery. Se me acabó mi batería sounds redundant. If you need to be specific, say la batería del móvil.

Are there more natural alternatives to say this in Spain?

Very common options:

Me quedé sin batería.
Se me apagó el móvil (porque se quedó sin batería).
No tenía batería.
Se me agotó la batería. Colloquial: Se me murió el móvil (informal, context-dependent).

Why is it no pude (preterite) and not no podía (imperfect)?

No pude responder = a specific completed event: at that moment, you couldn’t and in fact didn’t answer.
No podía responder = ongoing background inability, describing the situation, not necessarily stating the outcome.
Example: Ayer no pude responder vs Ayer, cuando me llamaste, no podía responder porque conducía.

Could I use the present perfect in Spain?

Yes. In Peninsular Spanish, the present perfect is common for “today” or still-relevant past:

Se me ha acabado la batería, así que no he podido responder. If it’s clearly “yesterday” or a finished timeframe, preterite is more natural:
Ayer se me acabó la batería, así que no pude responder.

Is así que the same as porque?

They express the same cause–effect relationship but from different sides:

Se me acabó la batería, así que no pude responder. (result)
No pude responder porque se me acabó la batería. (cause) Both are correct; choose the one that fits your flow of information.

Should there be a comma before así que?

Yes, it’s standard to place a comma before así que when it links two clauses: ..., así que ...

Why responder a tu llamada and not responder tu llamada?

With the meaning “respond to,” responder normally takes a: responder a una llamada. For phone calls, however, the most idiomatic verb to mean “answer (pick up)” is contestar (transitive) or, in Spain, coger (el teléfono):

No pude contestar tu llamada.
No pude coger el teléfono.

Is responder a tu llamada the most natural choice for phones?

It’s correct but can sound a bit formal/less idiomatic for “answering a ringing phone.” In Spain, people typically say:

No pude contestar tu llamada.
No pude coger tu llamada / el teléfono. Also common: No pude atender tu llamada.

Where can I place the pronoun: no te pude responder or no pude responderte?

Both are correct:

Before the conjugated verb: No te pude responder.
Attached to the infinitive: No pude responderte. With phone vocabulary:
No te pude contestar / No pude contestarte.
In Spain: No te pude coger el teléfono.
Using a direct object pronoun with contestar works: No pude contestarla (la llamada). With responder, responderla is far less common here.

How do I make it formal with usted?

Change the possessive/pronoun to su/usted:

Se me acabó la batería, así que no pude responder a su llamada.
Alternatives: ... no pude atender su llamada., ... no pude cogerle el teléfono.

Why is tu (possessive) written without an accent, but tú (you) has one?

tu (no accent) = “your” (possessive): tu llamada.
tú (with accent) = “you” (subject pronoun): Tú no contestaste.
In the sentence, tu is possessive, so no accent.

Is se me acabó reflexive?

No. se here is part of the pronominal verb acabarse (“to run out”), and me is an indirect object showing who’s affected. The subject is la batería. This pattern is often called the “accidental se.”

Can I change the word order to La batería se me acabó?

Yes. Both Se me acabó la batería and La batería se me acabó are correct. Starting with Se me acabó highlights the event; starting with La batería highlights the topic (battery).

How do I express the state instead of the event?

Event (it ran out at some point): Me quedé sin batería. / Se me acabó la batería.
State (the battery was low/empty): No tenía batería. / Tenía la batería descargada.

Any regional cautions?

Yes. In Spain, coger (el teléfono) is perfectly normal for “pick up.” In much of Latin America, coger can be vulgar; use contestar, atender or responder instead.