Learn Hardcore Russian: Моя зарядка для телефона осталась дома.

дома is an adverb meaning “at home.” No preposition. It answers “where?”
в доме = “in the house” (inside a specific house/building).
домой = “(to) home,” motion toward home; it answers “where to?” Pronunciation tip: домá (stress on the second syllable) = “at home,” while до́ма (stress on the first) is the plural noun “houses.”

What case is телефона and why?

It’s genitive singular. The preposition для (“for”) always takes the genitive: для телефона = “for a/the phone.” Base form: телефон → genitive телефона.

Can I say зарядка телефона or зарядка к телефону instead of для телефона?

зарядка телефона can mean “the phone’s charger,” but it can also mean “the phone’s charging (process).” It’s fine, but potentially ambiguous.
зарядка к телефону (with к
- dative) is used about accessories (“for/compatible with a phone”), somewhat old‑fashioned/advertising style.
Colloquial: зарядка от телефона = “the charger that came with/for the phone.” For clear, general purpose, для телефона is the safest.

What’s the difference between зарядка осталась дома and я оставил(а) зарядку дома or я забыл(а) зарядку дома?

…осталась дома = “(it) ended up staying at home,” focuses on the result; no explicit agent/blame.
я оставил(а)… = “I left (it) at home,” emphasizes your action (transitive verb).
я забыл(а)… = “I forgot (it) at home,” explicitly about forgetting. All are natural; pick the nuance you want.

Does зарядка always mean “charger”?

No. зарядка can mean:

a charger,
the act of charging,
morning exercise/gym routine. For unambiguous “charger,” use зарядное устройство (neutral/formal). Colloquial: зарядник, or шнур/кабель для телефона (cord/cable).

Is моя necessary?

Not always. Russian often omits possessives when ownership is obvious:

Зарядка для телефона осталась дома. Using моя adds emphasis that it’s yours (useful if several chargers are being discussed).

Can I change the word order?

Yes, for emphasis:

Neutral: Моя зарядка для телефона осталась дома.
Emphasize location: Дома осталась моя зарядка для телефона.
Without possessive: Зарядка для телефона осталась дома. Placing дома at the end is most common in neutral style.

Why perfective осталась, not imperfective оставалась?

Aspect:

осталась (perfective) = a single completed result: it ended up remaining at home.
оставалась (imperfective) = was remaining/used to remain (duration or habit). That doesn’t fit a one‑off “I forgot it” situation.

What does the -сь ending in осталась do?

It’s the reflexive/mediopassive marker -ся/-сь. With it, остаться is intransitive “to remain, stay.” Without it, оставить is transitive “to leave (something)”:

Зарядка осталась дома. (It remained at home.)
Я оставил(а) зарядку дома. (I left the charger at home.)

Any pronunciation/stress gotchas here?

заря́дка (stress on -ряд-), not за́рядка.
телефо́на (stress on -фон-).
домá for “at home” (stress on the second syllable); beware до́ма = “houses.”

Can I omit для телефона?

Yes, if context makes it clear: Моя зарядка осталась дома. If multiple devices are possible, для телефона clarifies it’s the phone’s charger (not a laptop or camera charger).

How would the sentence change with a different noun gender?

Neuter: Моё зарядное устройство осталось дома.
Masculine: Мой кабель остался дома. The past-tense verb agrees with the subject’s gender: осталось/остался/осталась/остались.

What case is зарядка here, and what changes if I say “I left the charger at home”?

Here зарядка is nominative (the subject): Зарядка осталась дома. With “I left…,” it becomes the direct object in the accusative: Я оставил(а) зарядку дома.

Can I say У меня дома осталась зарядка?

Yes. У меня дома… emphasizes “at my place (not someone else’s).” It’s natural for contrast: У меня дома осталась (моя) зарядка для телефона.