Ladekurven og ladehastigheten endrer seg.

Because Norwegian usually makes compound nouns by joining words together.

• ladekurve = charging curve
• ladehastighet = charging speed

This is very normal in Norwegian. Where English often uses two words, Norwegian often uses one:

• charging speed → ladehastighet
• car door → bildør
• power cable → strømkabel

So lade- is attached directly to the main noun.

Lade- comes from å lade, which means to charge.

In compounds, lade- works like English charging or charge-:

• ladekurve = charging curve
• ladehastighet = charging speed
• ladekabel = charging cable

So it is not a separate adjective here; it is the first part of a compound noun.

The ending -en is the definite article attached to the noun. It usually corresponds to English the.

So:

• en ladekurve = a charging curve
• ladekurven = the charging curve

and

• en ladehastighet = a charging speed
• ladehastigheten = the charging speed

In this sentence, both nouns are definite, so the meaning is the charging curve and the charging speed.

Because in Norwegian, the is often added to the end of the noun instead of being written as a separate word.

Compare:

• English: the speed
• Norwegian: hastigheten

This is one of the biggest structural differences from English.

Very roughly:

• en hastighet = a speed
• hastigheten = the speed

So ladekurven og ladehastigheten already includes the idea of the twice.

Endrer seg means changes or is changing in the sense of changes itself / changes on its own.

The verb is å endre = to change / to alter.
But Norwegian often uses the reflexive form endre seg when something changes itself or undergoes change.

Compare:

• Jeg endrer planen. = I change the plan.
  
  • Here, something is being changed.
• Planen endrer seg. = The plan changes.
  
  • Here, the plan itself changes.

So in your sentence:

• Ladekurven og ladehastigheten endrer seg.

the idea is that these things change.

In English, you might think of it as themselves, because there are two things: the charging curve and the charging speed.

But in Norwegian, seg is the normal reflexive form for third person, and it is used very broadly. You do not need a different form here.

So:

• singular third person: seg
• plural third person: seg

That means seg can correspond to English himself, herself, itself, or themselves, depending on context.

Because Norwegian verbs do not change form for singular vs. plural subjects in the present tense.

English:

• it changes
• they change

Norwegian:

• den endrer seg
• de endrer seg

The verb form stays endrer.

So even though the subject is made of two nouns joined by og (and), the verb does not change.

Endrer is the present tense of å endre.

Depending on context, Norwegian present tense can correspond to English:

• changes
• is changing
• sometimes even a general present like does change

So:

• Ladekurven og ladehastigheten endrer seg.

can mean:

• The charging curve and the charging speed change
• The charging curve and the charging speed are changing

The exact English choice depends on context.

Yes. This is a very normal subject + verb main clause.

• Ladekurven og ladehastigheten = subject
• endrer seg = verb phrase

So the structure is:

• [Subject] + [Verb]

That is the basic Norwegian word order in a simple statement.

If you put another element first, Norwegian would normally move the verb into second position:

• Over tid endrer ladekurven og ladehastigheten seg.
  = Over time, the charging curve and the charging speed change.

That is the usual V2 pattern in Norwegian main clauses.

If you want indefinite singular, you would use en:

• En ladekurve og en ladehastighet endrer seg.

That would mean something like a charging curve and a charging speed change, which is less natural unless you are speaking very generally.

If you want definite plural, you would change the nouns:

• Ladekurvene og ladehastighetene endrer seg.
• The charging curves and the charging speeds change / are changing.

So the original sentence uses definite singular for both nouns:

• ladekurven = the charging curve
• ladehastigheten = the charging speed

Og simply means and.

It joins the two nouns into one compound subject:

• ladekurven og ladehastigheten

So the sentence is talking about both things together:

• the charging curve
• and the charging speed

They are treated as a combined subject before the verb.