eonnineun hyudaeponi kkeojilkka bwa chungjeonseonirang bojobaeteorireul hangsang gabange neoheo dwo.

In Korean, family terms often appear without an explicit possessive when the relationship is obvious from context.

So:

• 언니는 ... naturally means As for my older sister...
• Korean usually does not need 내 언니는 unless you want extra emphasis or contrast.

Also, 언니 is used by a female speaker for:

• her older sister
• sometimes an older female friend or close older woman

If the speaker were male, he would normally say 누나, not 언니.

언니 literally means older sister, but only from a female speaker’s point of view.

So in this sentence, the speaker is most naturally understood as female, and 언니 means:

• my older sister, or
• depending on context, possibly an older female acquaintance the speaker calls 언니

If this is just a textbook sentence with no extra context, my older sister is the safest interpretation.

는 is the topic marker.

So 언니는 means something like:

• as for my older sister
• my older sister, (she)...

It sets 언니 up as the topic of the sentence. It can also give a slight contrastive feeling depending on context, like:

• As for my older sister, she always keeps...

In this sentence, it mainly just introduces who we are talking about.

Because inside 휴대폰이 꺼질까 봐, the phone is the thing that might turn off.

So:

• 휴대폰이 = the phone as the subject of 꺼지다
• 꺼지다 is an intransitive verb, meaning to turn off / go off

This part is a subordinate clause:

• 휴대폰이 꺼질까 봐 = because she’s worried the phone might die / in case the phone dies

So the phone is not being acted on directly; it is the thing that may undergo the action of turning off.

꺼지다 literally means to go out, to be turned off, or to switch off.

With electronics, it often means:

• to turn off
• to die
• to run out of battery and shut off

So here:

• 휴대폰이 꺼지다 = the phone turns off / the phone dies

This is different from 끄다, which is the transitive verb:

• 휴대폰을 끄다 = to turn off the phone

A useful contrast:

• 불이 꺼졌어요 = The light went out
• 불을 껐어요 = I turned off the light

-ㄹ까 봐 / -을까 봐 means something like:

• for fear that...
• because (someone is) worried that...
• in case...

So:

• 꺼질까 봐 = for fear that it might turn off
• because she’s worried it might turn off
• in case it dies

Formation here:

• dictionary form: 꺼지다
• verb stem: 꺼지-
• since the stem ends in a vowel, use -ㄹ까 봐
• 꺼질까 봐

This pattern is often followed by a precautionary action:

• worried X might happen → so I do Y

That is exactly what happens here:

• phone might die → so she keeps a cable and power bank in her bag

They are not the same.

-(으)면 means:

• if
• when
• a neutral condition

Example:

• 휴대폰이 꺼지면 충전해.
• If the phone dies, I charge it.

But -ㄹ까 봐 includes:

• worry
• possibility
• often a sense of preventive action

Example:

• 휴대폰이 꺼질까 봐 충전기를 가져가.
• I take a charger because I’m worried my phone might die / in case it dies.

So in your sentence, -ㄹ까 봐 is better because she is preparing ahead of time out of concern.

Yes, 이랑 here means and between nouns.

So:

• 충전선이랑 보조배터리 = a charging cable and a power bank

About 이랑:

• casual spoken style
• can also mean with, depending on context

Other ways to say and with nouns:

• 하고 — casual/common
• 와/과 — a bit more formal or written
• 및 — very formal, written

So these are similar:

• 충전선이랑 보조배터리
• 충전선하고 보조배터리
• 충전선과 보조배터리

In everyday speech, 이랑 sounds very natural.

Because 충전선이랑 보조배터리 forms one combined noun phrase:

• the charging cable and power bank

That whole phrase is the object of 넣어 두다, so the object marker appears once at the end:

• 충전선이랑 보조배터리를

This is very normal in Korean.

It works like:

• 책이랑 노트를 샀어.
• I bought a book and a notebook.

You do not normally say:

• 책을이랑 노트를 ❌

The marker goes on the whole coordinated phrase.

보조배터리 literally means auxiliary battery.

In natural English, it usually means:

• power bank
• portable battery
• sometimes portable charger

So in this sentence, it refers to a battery pack you carry around to charge your phone when needed.

This is a very important nuance.

넣다 = to put in

넣어 두다 = to put in and leave it there / keep it there / put it away in advance for later use

So:

• 가방에 넣어 = put it in the bag
• 가방에 넣어 둬 = keep it in the bag / put it in the bag and leave it there ready

In this sentence, 넣어 둬 suggests a habitual state of preparedness:

• she keeps those items in her bag all the time
• not just one momentary action of placing them there

This is why 두다 is used: it often adds the meaning of doing something in advance or leaving something in a certain state.

둬 is a casual, non-polite spoken form.

The full verb is:

• 두다

In this construction:

• 넣어 두다 → 넣어 둬 in casual speech

So the sentence ends in a conversational 반말 style. That means the speaker is talking:

• casually to a friend
• casually in narration
• or in an informal context

Possible style equivalents:

• 넣어 둬 — casual
• 넣어 둬요 — polite
• 넣어 둔다 — plain written/dictionary-style statement
• 넣어 둡니다 — formal polite

So this sentence is informal spoken Korean.

It tells you this is a habit, not a one-time action.

• 항상 = always
• 가방에 = in the bag

So the idea is:

• she always keeps them in her bag
• this is something she regularly does as a precaution

Without 항상, the sentence could still mean she keeps them in her bag, but 항상 makes the habitual meaning much clearer.

It breaks down like this:

• 언니는 — as for my older sister
• 휴대폰이 꺼질까 봐 — because she’s worried her phone might die / in case her phone dies
• 충전선이랑 보조배터리를 — a charging cable and a power bank
• 항상 가방에 — always in her bag
• 넣어 둬 — keeps / puts and leaves there

So the sentence follows a very common Korean pattern:

[topic] + [reason/concern clause] + [object] + [location] + [verb]

That kind of order is very natural in Korean, especially when giving the reason before the main action.