Als het lampje blijft knipperen, moet de batterij vervangen worden.

Because lampje is a diminutive form of lamp.

In Dutch, diminutives are usually made with endings like -je, -tje, -pje, or -etje, and all diminutives take the article het.

• de lamp = the lamp
• het lampje = the little lamp / indicator light

So even though lamp is a de-word, lampje becomes a het-word.

Literally, lampje means little lamp, but in practical Dutch it often refers to a small light, especially an indicator light on a device.

So in this sentence, het lampje probably means something like:

• the indicator light
• the little warning light

It does not necessarily mean a physical lamp in a room.

Als means if here.

It introduces a condition:

• Als het lampje blijft knipperen = If the light keeps flashing

This is very common in instructions and manuals:

• Als X gebeurt, moet je Y doen
  = If X happens, you must do Y.

In some contexts, als can also mean when, but here if is the most natural interpretation.

Because als introduces a subordinate clause, and in Dutch subordinate clauses, verbs typically move toward the end.

So:

• het lampje = subject
• blijft knipperen = verb cluster at the end

Compare:

• Main clause: Het lampje blijft knipperen.
• Subordinate clause: Als het lampje blijft knipperen, ...

This verb-final pattern is one of the most important features of Dutch word order.

Blijven + infinitive means to keep doing something or to continue doing something.

So:

• blijven = to remain / stay
• knipperen = to blink / flash
• blijft knipperen = keeps blinking / continues flashing

Some examples:

• Hij blijft praten. = He keeps talking.
• Het blijft regenen. = It keeps raining.
• Het lampje blijft knipperen. = The light keeps flashing.

In this kind of sentence, knipperen is the normal word for a light that blinks or flashes on and off.

• knipperen = blink, flash
• flikkeren = flicker

Flikkeren often suggests an unsteady or irregular light, while knipperen is the usual word for a warning light or indicator.

So for a battery warning light, knipperen is the expected choice.

Because the sentence begins with the als-clause, and Dutch main clauses follow the verb-second rule.

The first position is taken by the whole subordinate clause:

• Als het lampje blijft knipperen

So the finite verb of the main clause must come next:

• moet

Then comes the subject:

• de batterij

So:

• Als het lampje blijft knipperen, moet de batterij vervangen worden.

If you put the main clause first, you get the more basic order:

• De batterij moet vervangen worden als het lampje blijft knipperen.

Both are correct.

This is a passive construction with a modal verb.

Break it down:

• moet = must
• vervangen = replace
• worden = be / become, used to form the passive

So:

• de batterij moet vervangen worden = the battery must be replaced

This is the passive equivalent of an active sentence like:

• Iemand moet de batterij vervangen. = Someone must replace the battery.

Dutch often uses worden to form the passive:

• De deur wordt gesloten. = The door is being closed.
• De batterij moet vervangen worden. = The battery must be replaced.

Yes. That is also correct.

Both are standard:

• De batterij moet vervangen worden
• De batterij moet worden vervangen

The meaning is the same: The battery must be replaced.

In practice, moet vervangen worden is very common and often sounds a bit more natural in everyday Dutch, but both word orders are used.

Because after moeten and worden in this structure, Dutch uses the infinitive, not a past participle.

So:

• vervangen = infinitive
• vervangen worden = to be replaced
• moet vervangen worden = must be replaced

This is because Dutch modal verbs like moeten, kunnen, willen, etc. are followed by an infinitive.

The form vervangd would not be correct here.
Also, the past participle of vervangen is actually vervangen as well, not vervangd.

Because batterij is a de-word in Dutch.

So:

• de batterij = the battery

This is just something you have to learn with the noun. Unfortunately, grammatical gender in Dutch is not always predictable.

Yes, the sentence is built with present-tense forms:

• blijft = present tense of blijven
• moet = present tense of moeten

But the overall meaning is more like a general instruction or rule, not just something happening right now.

So it means something like:

• If the light keeps flashing, the battery needs to be replaced.

This is very common in manuals, instructions, and warnings.

Yes.

You can say:

• Als het lampje blijft knipperen, moet de batterij vervangen worden.
• De batterij moet vervangen worden als het lampje blijft knipperen.

Both are correct.

The difference is mainly emphasis and style:

• Starting with Als... foregrounds the condition.
• Starting with De batterij... foregrounds the action that needs to be taken.

Not always.

In Dutch, moeten can mean:

• must
• have to
• need to

In instruction manuals, moet often sounds a bit less forceful than English must can sound. It often simply expresses necessity:

• De batterij moet vervangen worden = The battery must be replaced / needs to be replaced

So depending on context, needs to be replaced may feel more natural in English, even though must be replaced is a direct translation.