Batteriet i mobilen är tomt, så jag måste ladda den innan mötet börjar.

Because Swedish is using the definite form here: the battery, not just a battery.

• ett batteri = a battery
• batteriet = the battery

Swedish usually puts definiteness on the noun itself with an ending. Since batteri is an ett noun, the definite singular form is -et.

Yes. i mobilen literally means in the phone.

That makes sense because the battery is physically inside the phone.

• i = in
• mobilen = the mobile/the phone

In natural English, we might say my phone or the phone, but Swedish often uses the definite form when the object is obvious from context.

Swedish often leaves out possessive words like my when it is already clear whose thing is being talked about.

So:

• Batteriet i mobilen = literally the battery in the phone
• but in context it can easily mean the battery in my phone

This is very common in Swedish, especially when the owner is obvious.

Because the adjective must agree with the noun’s gender and number.

Here, batteriet comes from ett batteri, so it is a neuter noun (ett noun). Neuter singular adjectives usually take -t in the basic predicate form.

• en mobil är tom = the phone is empty/dead
• ett batteri är tomt = the battery is empty/dead

So tomt matches batteriet.

Yes. Literally, tomt means empty, but with batteries it is a normal Swedish way to say the battery is dead, flat, or out of charge.

So:

• Batteriet är tomt = The battery is dead / flat / empty

It may sound slightly different from English, but it is very natural in Swedish.

Because så here is being used as a coordinating conjunction, meaning so.

Coordinating conjunctions do not cause inversion in Swedish. So the word order stays like a normal main clause:

• jag måste ladda den = I must charge it

Compare:

• Batteriet är tomt, så jag måste ladda den.
  The battery is dead, so I have to charge it.

But if you used an adverb like därför (therefore), inversion would happen:

• Batteriet är tomt. Därför måste jag ladda den.

So this is a very useful word-order distinction.

After modal verbs like måste (must / have to), Swedish normally uses the infinitive without att.

So:

• jag måste ladda = I must charge
• jag kan ladda = I can charge
• jag vill ladda = I want to charge

This is similar to English, where we also say must charge, not must to charge.

In this sentence, den most naturally refers to mobilen (the phone), not batteriet.

That is why it is den:

• mobilen is an en noun → pronoun den
• batteriet is an ett noun → pronoun det

So the logic is:

• The battery in the phone is dead, so I need to charge it
  = charge the phone → ladda den

If you specifically meant the battery, you would expect det instead.

This is a very common thing in Swedish: the pronoun agrees with the noun it refers to, not with an English idea of it.

Yes, absolutely.

• Jag måste ladda batteriet = I have to charge the battery
• Jag måste ladda den = I have to charge it

But in everyday speech, people often say they are charging the phone, not specifically the battery, even though the battery is what actually needs power. So ladda den referring to mobilen sounds very natural.

Because innan means before, and here it introduces a subordinate clause:

• innan mötet börjar = before the meeting starts

In Swedish subordinate clauses, the word order is different from main clauses in some situations, and learners often notice that the verb comes later than they expect.

Here the structure is:

• innan = subordinating conjunction
• mötet = subject
• börjar = verb

So literally: before the meeting starts

This is normal Swedish clause structure.

Because Swedish often uses the present tense for future events when the time is already clear from context.

Here, innan mötet börjar refers to a future event, but Swedish does not need a special future form.

So:

• mötet börjar = the meeting starts / is starting
• in context: before the meeting starts

This works much like English in sentences such as:

• I’ll call you before the meeting starts.

So the present tense is completely natural here.

Because it means a specific meeting that both speaker and listener can identify from context.

• mötet = the meeting
• ett möte = a meeting

So:

• innan mötet börjar = before the meeting starts
• innan ett möte börjar would mean before a meeting starts, which is more general or less specific

In this sentence, the speaker clearly has a particular meeting in mind.

Sometimes, but not in exactly the same way.

• innan is commonly used before a clause:
  • innan mötet börjar = before the meeting starts
• före is commonly used before a noun phrase:
  • före mötet = before the meeting

So in this sentence, innan is the natural choice because it is followed by mötet börjar, a full clause with a verb.

If you changed the structure, you could say:

• Jag måste ladda den före mötet.
  I have to charge it before the meeting.

Both are correct, but they are structured differently.