Learn Hardcore Indonesian: Saya membawa pengisi daya di tas, kalau-kalau baterai habis. - I bring a charger in my bag, just in case the battery runs out.

kalau-kalau means “just in case,” expressing a precaution for a possible event that may or may not happen.
It’s perfectly correct, slightly bookish/explicit.
Very common everyday alternatives:
- (untuk) jaga-jaga = as a precaution. Example: “Saya bawa charger (untuk) jaga-jaga.”
- jaga-jaga kalau … = as a precaution if …
- siapa tahu … = who knows, maybe …
- Colloquial: takut … = (because I’m worried) in case … (“… takut baterai habis.”)

Can I just use kalau instead of kalau-kalau?

Yes. Many people say “…, kalau baterai habis.” Context supplies the “just in case” nuance. Using kalau-kalau makes the precaution meaning explicit, but kalau alone is very common and natural.

Does the comma before kalau-kalau have to be there?

By the book (PUEBI): when the “if/when” clause comes after the main clause, a comma is usually not required: “Saya membawa … kalau(-kalau) baterai habis.”
If the clause comes first, use a comma: “Kalau(-kalau) baterai habis, saya membawa …”
In real-world writing, many people keep the comma after the main clause to mark the pause. It’s widely accepted.

Does di tas mean “in my bag”? Should it be di dalam tas?

di tas commonly means “in the bag” (and from context, usually “in my bag”). It’s fine in everyday speech.
di dalam tas explicitly means “inside the bag” and is a bit more precise.
To make “my” explicit, say di tas saya or di dalam tas saya.
“on the bag” would be di atas tas, not di tas.

Is pengisi daya really what people say for “charger”?

pengisi daya is the standard/official term (you’ll see it in manuals, news, tech writing).
In daily life, people very often say:
- charger (most common)
- casan (slang, from “charge”/“ngecas”)
All are understood. Choose based on formality:
- Formal/neutral: pengisi daya
- Everyday: charger
- Very casual: casan

Is baterai habis the normal way to say “the battery is dead”? Should I use mati?

baterai habis = the battery is used up/out of power. Very natural.
baterainya habis (with -nya) is also very idiomatic: “the battery’s dead.”
HP-nya mati = the phone is off/dead (often because the battery ran out). You can also hear baterainya mati, but habis is more standard for batteries.
Slang: lowbat (from “low battery”).
Standard spelling is baterai (not “batere/batre” in writing, though those appear in speech).

How do I make it explicitly “my bag” or “my phone battery”?

My bag: di tas saya (neutral/polite), di tasku (informal), di tas gue (Jakarta casual).
My phone battery: baterai HP saya, baterai ponsel saya, or simply baterainya if context is clear.

Why is there no word for “a” before “charger” in Indonesian?

Indonesian has no articles like “a/an/the.” Saya membawa pengisi daya already means “I carry a charger.” If you want to emphasize quantity, you can add a numeral or classifier, e.g., satu/ sebuah pengisi daya, but it’s not normally needed here.

Can I say bawa instead of membawa? And what’s the difference with membawakan?

membawa is the formal/complete verb “to carry/bring.”
bawa is the base form, very common in casual speech: Saya/Aku bawa charger …
membawakan means “to bring (something) for someone” or “to perform (a song).” Use it when there’s a beneficiary: Saya membawakan charger untuk kamu (I brought a charger for you). Don’t use membawakan if you just mean you’re carrying it yourself.

Why is di written separately in di tas?

di as a preposition (at/in/on) is written separately: di tas, di rumah, di dalam.
di- as a passive verb prefix is attached to verbs: dibawa (is/was carried), ditaruh (is/was put).
So: di tas (space), but dibawa (no space).

Can I move parts of the sentence around?

Yes. Some natural options:

Saya membawa pengisi daya di tas kalau(-kalau) baterai habis. (no comma)
Kalau(-kalau) baterai habis, saya membawa pengisi daya di tas.
You can also front the location for emphasis: Di tas, saya membawa pengisi daya … (stylistic, less common in speech).

Could I express this with a purpose clause like agar/supaya?

Yes, but you’d normally add what the purpose is:

Saya membawa pengisi daya di tas supaya/agar bisa mengecas kalau baterai habis. This means “so that I can charge if the battery runs out.” It’s a purpose construction rather than pure “just in case.”

Any quick pronunciation tips for key words?

baterai: ba-te-rai (final “ai” like English “eye”).
kalau-kalau: ka-lau ka-lau (au like “ow” in “cow”).
pengisi: pə-ngí-si (the “ng” is like in “sing”).
daya: da-ya (both vowels clear).
tas: like “tahs.”
saya: sah-yah (both syllables clear).

What are some natural, casual rewrites of the whole sentence?

Aku bawa charger di tas, jaga-jaga kalau baterainya habis.
Gue bawa casan di tas, siapa tahu baterai HP gue habis.
Saya bawa pengisi daya di dalam tas, untuk jaga-jaga.
Saya bawa charger di tas, takut baterai habis.