Min dator har en stor skärm, men batteriet måste laddas ofta.

Because dator is an en-word in Swedish.

For singular nouns:

• min is used with en-words
• mitt is used with ett-words
• mina is used with plurals

So:

• min dator = my computer
• mitt batteri = my battery
• mina datorer = my computers

In Swedish, a possessive usually replaces the article.

So you say:

• min dator = my computer

Not:

• min en dator

This works like:

• min bok = my book
• mitt hus = my house
• mina vänner = my friends

That is just part of the word itself. Dator is singular.

This can definitely confuse learners, because -or is also a common plural ending in Swedish. But here:

• en dator = a computer
• datorer = computers
• datorn = the computer
• datorerna = the computers

So the -or in dator is not a plural ending.

Because skärm is an en-word and it is singular and indefinite here.

That gives:

• article: en
• adjective form: stor

So:

• en stor skärm = a big screen

If it were an ett-word, the adjective would change:

• ett stort batteri = a big battery

It changes to match the noun.

Common basic pattern:

• en stor skärm = a big screen
• ett stort batteri = a big battery
• stora skärmar = big screens
• stora batterier = big batteries

So:

• stor for en-word singular
• stort for ett-word singular
• stora for plural, and also for definite forms in many cases

Batteriet is the definite singular form of batteri.

• ett batteri = a battery
• batteriet = the battery

In Swedish, the definite article is often attached to the end of the noun as a suffix.

Here, -et is the definite ending for this ett-word:

• batteri → batteriet

So the sentence is talking about a specific battery: the battery of the computer.

Swedish uses har for possession, just like English uses have.

So:

• Min dator har en stor skärm = My computer has a big screen

You do not use är for possession.
Är means is/are.

Compare:

• Datorn är stor = The computer is big
• Datorn har en stor skärm = The computer has a big screen

It is a passive construction.

• måste = must
• laddas = be charged

So:

• batteriet måste laddas = the battery must be charged

The verb ladda means to charge.
Adding -s here makes it passive:

• ladda = charge
• laddas = be charged

Here it is passive, not reflexive.

That is an important distinction, because Swedish -s forms can look unusual to English speakers.

In this sentence:

• batteriet måste laddas = the battery must be charged

The battery is receiving the action, so this is passive.

An active version would be:

• Jag måste ladda batteriet = I must charge the battery

Because after a modal verb such as måste, Swedish normally uses the infinitive form of the main verb.

Examples:

• Jag måste gå = I must go
• Du måste läsa = You must read
• Batteriet måste laddas = The battery must be charged

So måste is the finite verb, and laddas stays in the infinitive/passive form.

Yes, both are possible.

In the sentence:

• batteriet måste laddas ofta

the adverb ofta comes after the verb phrase and sounds very natural.

You can also say:

• batteriet måste ofta laddas

That is also correct. The difference is mostly one of rhythm or emphasis, not basic meaning.

Very roughly:

• måste laddas ofta = a neutral statement
• måste ofta laddas = slightly more focus on often

Because men is a coordinating conjunction, and the clause after it keeps normal main-clause word order.

So:

• Min dator har en stor skärm, men batteriet måste laddas ofta.

The second clause begins like a regular statement:

• batteriet = subject
• måste = finite verb

Swedish main clauses usually put the finite verb in second position, and that is exactly what happens here.

The tricky part is the beginning: sk before ä is pronounced with a sh-like Swedish sound.

A rough guide:

• skärm sounds approximately like shairm, but with a more Swedish sound than English sh

A few points:

• sk before e, i, y, ä, ö often has this soft sound
• ä is somewhat like the vowel in bed, though exact pronunciation depends on accent
• the word has one syllable

So the hardest part for most learners is the initial sk sound.

Not always.

In modern Swedish, a comma before men is often optional, especially in short, clear sentences. Many writers include it, and many leave it out.

So both of these are acceptable:

• Min dator har en stor skärm, men batteriet måste laddas ofta.
• Min dator har en stor skärm men batteriet måste laddas ofta.

The version with the comma can make the pause between the two clauses clearer.