Moja baterija je prazna, pa nosim punjač sa sobom.

Because baterija is a feminine noun in Serbian, and the possessive adjective moj (my) has to agree with it in gender, number, and case.

So:

• moj = masculine singular
• moja = feminine singular
• moje = neuter singular

Since baterija is feminine singular, you say moja baterija.

For the same reason: prazna has to agree with baterija.

The adjective prazan means empty, but it changes form:

• prazan = masculine
• prazna = feminine
• prazno = neuter

Since baterija is feminine, you use prazna:
Moja baterija je prazna.

In natural English, this often means my battery is dead/flat, even though the literal Serbian adjective is empty.

Je is the 3rd person singular present tense of the verb biti (to be).

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In Moja baterija je prazna, je means is.

Here pa means something like so, therefore, or and so.

It connects the two ideas:

• Moja baterija je prazna = My battery is dead/empty
• pa nosim punjač sa sobom = so I carry a charger with me

So pa introduces a result or consequence.

It is very common in everyday Serbian and often sounds natural and conversational.

Not with the same meaning.

• pa = so, and so, showing a result
• jer / zato što = because, giving a reason

Your sentence means:

• My battery is dead, so I carry a charger with me.

If you used jer or zato što, the logic would change:

• Nosim punjač sa sobom jer mi je baterija prazna.
  = I carry a charger with me because my battery is dead.

That is also correct, but it is structured differently.

Nosim is the 1st person singular present tense of nositi, which means to carry, to wear, or sometimes to take around with you, depending on context.

Here it means I carry / I’m carrying.

Conjugation:

• ja nosim = I carry
• ti nosiš = you carry
• on/ona nosi = he/she carries

In Serbian, the present tense often covers both English I carry and I am carrying, depending on context.

Because punjač is the direct object of nosim, and for a masculine inanimate noun, the accusative singular is the same as the nominative singular.

So:

• nominative: punjač
• accusative: punjač

That is why the form does not change.

If the direct object were a feminine noun, you would often see a clearer change. For example:

• nosim torbu = I carry a bag

Punjač means charger.

It comes from the verb puniti, which means to fill or to charge.

So learners often notice a useful connection:

• puniti = to charge/fill
• punjač = charger
• prazan/prazna = empty

That makes the sentence easy to remember: the battery is empty, so you carry a charger.

Sa sobom literally means with oneself, but in normal English it is usually translated as with me/you/him/her, depending on the subject.

In this sentence, the subject is I, so:

• nosim punjač sa sobom = I carry a charger with me

The word sobom comes from the reflexive pronoun sebe/soba, used when the object refers back to the subject.

This is very common in Serbian:

• Nosim pasoš sa sobom. = I carry my passport with me.
• Ona nosi torbu sa sobom. = She carries a bag with her.

Both s and sa mean with, but sa is often used for easier pronunciation, especially before certain consonants or consonant clusters.

Since sobom begins with s, Serbian normally uses:

• sa sobom

This sounds smoother than s sobom.

So this is mainly a pronunciation-based choice.

Yes. You could say:

• Baterija mi je prazna, pa nosim punjač sa sobom.

That is also very natural, and in many situations it may even sound more typical.

The difference is mainly one of style and emphasis:

• Moja baterija je prazna... emphasizes my battery
• Baterija mi je prazna... is a very common Serbian way to say my battery is dead

So the original sentence is correct, but it is not the only natural option.

Yes, Serbian word order is quite flexible.

The sentence:

• Moja baterija je prazna, pa nosim punjač sa sobom.

is a normal, clear order. But Serbian can move things around for emphasis or style.

For example:

• Prazna mi je baterija, pa nosim punjač sa sobom.
• Punjač nosim sa sobom, jer mi je baterija prazna.

These can all be correct in the right context.

Compared with English, Serbian relies more on case endings and agreement, so word order is freer.

It can absolutely mean a phone battery, a laptop battery, or another rechargeable battery, depending on context.

In everyday modern Serbian, if someone says:

• Baterija mi je prazna

people will often understand it as my phone battery is dead, especially if the context involves a phone.

So the word is broad, just like battery in English.