eoje bame hyudaeponeul chungjeonhaji moshaeseo jigeum chinguege mesijireul mos bonaeyo.

-을/를 marks the direct object.

• 휴대폰을 충전하다 = “to charge the phone” (phone = thing being charged)
• 메시지를 보내다 = “to send a message” (message = thing being sent)

• 충전하지 못해서 = “because I couldn’t charge it” (inability / circumstances prevented it)
• 충전하지 않아서 = “because I didn’t charge it” (choice / intention, or just plain negation)

So 못해서 implies “I wasn’t able to,” not simply “I didn’t.”

-아서/어서 connects clauses and often means because / so (cause → result).
Here, 못해서 is 못하다 + -아서:

• (어제 밤에) 충전하지 못해서 = “because I couldn’t charge it (last night),” leading to the result:
• 지금 … 못 보내요 = “I can’t send … now.”

Yes, it’s normal and natural here because they describe two different “inabilities”: 1) 충전하지 못해서: couldn’t charge the phone last night (cause)
2) (지금) 못 보내요: can’t send a message now (result)

English might also say: “I couldn’t charge my phone last night, so I can’t message my friend now.”

Both mean “can’t send,” but nuance differs:

• 못 보내요: common, conversational, often implies practical difficulty or inability
• 보낼 수 없어요: more explicit “it’s not possible to send,” sometimes a bit more formal or emphatic

In this sentence, 못 보내요 sounds very natural.

Because send uses a recipient:

• 친구에게 = “to my friend” (recipient; -에게 is “to” for a person)
• 메시지를 = the thing being sent (direct object)

So the structure is basically: [recipient]-에게 + [thing]-를 + 보내다.

Yes.

• 친구에게: neutral / slightly more formal
• 친구한테: more casual, very common in speech

Both mean “to (my) friend” and fit this sentence.

Korean often omits the subject when it’s obvious from context. This sentence naturally implies I.
If you want to include it:

• 저는 어제 밤에 휴대폰을 충전하지 못해서 지금 친구에게 메시지를 못 보내요.
  Including 저는 adds a bit of emphasis/contrast (“As for me…”), but it isn’t required.