Learn Hardcore Croatian: Nakon dugog videopoziva potpuno sam ispraznio bateriju na tabletu. - After a long video call I completely drained the battery on the tablet.

After the preposition nakon (after), Croatian always uses the genitive case. So both the adjective and the noun change to genitive singular masculine:

dug → dugog
videopoziv → videopoziva

So nakon dugog videopoziva literally means after (of) a long video call, which in natural English is simply after a long video call.

Is there any difference between nakon dugog videopoziva and poslije dugog videopoziva?

In this sentence, they are practically interchangeable:

nakon dugog videopoziva
poslije dugog videopoziva

Both mean after a long video call and both require the genitive.

Nuance:

nakon can sound a bit more neutral or slightly stylistically “cleaner”.
poslije is extremely common in everyday speech.

You can safely use either here; the rest of the sentence stays the same.

Could I write video poziva as two words instead of videopoziva?

In modern standard Croatian, the preferred spelling is videopoziv (one word), so the genitive is videopoziva.

You might sometimes see video poziv written as two words, but:

As a compound noun meaning a specific thing (a video call), dictionaries and school grammars treat videopoziv as one word.
In your sentence, videopoziva is the correct and standard form.

So you should learn and use videopoziv – videopoziva – videopozivu… as a regular masculine noun.

How would the sentence change if the speaker is a woman?

Only the past participle of the verb changes to agree with the gender of the subject.

Original (male speaker):

Nakon dugog videopoziva potpuno sam ispraznio bateriju na tabletu.

Female speaker:

Nakon dugog videopoziva potpuno sam ispraznila bateriju na tabletu.

Changes:

ispraznio (masculine singular) → ispraznila (feminine singular)

The auxiliary sam stays the same, and all other words stay the same.

Why is it potpuno sam ispraznio, not sam potpuno ispraznio? Where does sam have to go?

Sam is a clitic form of the verb biti (to be) used here as an auxiliary in the past tense (perfekt). Croatian clitics (like sam, si, je, smo, ste, su) have a fairly fixed position:

They normally go in second position in the clause (after the first stressed word or phrase).

In your sentence:

First stressed element: Nakon dugog videopoziva (a whole phrase)
Then comes the clitic: sam
Then the main verb: ispraznio

So:

Nakon dugog videopoziva potpuno sam ispraznio… – natural
You could also say:
Nakon dugog videopoziva sam potpuno ispraznio… – also possible, but sam still tries to stay in that early “second position”.

What you generally cannot do is push sam to the very end or treat it like a normal stressed word. It must stay among the first elements of the clause.

Why is it ispraznio and not just praznio?

The verb here is isprazniti (perfective) = to empty / to drain completely.

prazniti (imperfective) suggests a process of emptying, not necessarily finished.
isprazniti (perfective) focuses on the completed result: it became empty.

In the past tense:

praznio sam – I was emptying / I used to empty (process, repeated, or unfinished)
ispraznio sam – I emptied / I drained completely (finished, one whole action)

Since the sentence talks about completely draining the battery as the result of a long video call, the perfective ispraznio is the natural choice.

What form is bateriju, and why does it end in -ju?

The dictionary form is baterija (battery), which is a feminine noun.

In ispraznio sam bateriju, bateriju is the direct object of the verb, so it is in the accusative singular feminine.

Declension (singular, key cases):

Nominative: baterija (subject)
Genitive: baterije
Dative: bateriji
Accusative: bateriju (object)
Locative: bateriji
Instrumental: baterijom

So the -ju ending is just the regular accusative singular ending for this type of feminine noun.

Why is it na tabletu and not na tablet?

The dictionary form is tablet (masculine noun).

After the preposition na, the case depends on the meaning:

na + accusative = movement to / onto something
na + locative = location on something (no movement)

Here, na tabletu means on the tablet (location), so you need na + locative:

Locative singular of tablet is tabletu → na tabletu

If you were expressing movement, for example Stavio sam futrolu na tablet (I put the cover onto the tablet), you would use na + accusative (na tablet), but that is a different sentence and meaning.

Do I need to say na svom tabletu or na mom tabletu instead of just na tabletu?

You can, but you don’t have to.

na tabletu – on the tablet (context usually makes it obvious that it’s your own tablet)
na svom tabletu – on my own tablet (reflexive possessive, referring back to the subject)
na mom tabletu – on my tablet (non‑reflexive possessive adjective)

In ordinary conversation, na tabletu is completely natural if the context is clear (for example, you are talking about your devices). If you want to emphasise that it was specifically your own tablet (not, say, a friend’s or a work device), you might say na svom tabletu or na mom tabletu.

How flexible is the word order in this sentence? Can I move parts around?

Croatian word order is more flexible than English because the grammar is shown by endings, not by position. You can move elements for emphasis or style.

All of these are grammatically possible and natural, with slightly different emphasis:

Nakon dugog videopoziva potpuno sam ispraznio bateriju na tabletu.
Potpuno sam ispraznio bateriju na tabletu nakon dugog videopoziva.
Bateriju na tabletu sam potpuno ispraznio nakon dugog videopoziva. (emphasis on the battery)
Nakon dugog videopoziva bateriju na tabletu sam potpuno ispraznio.

The main restriction is the placement of clitics (sam); they must stay very early in the clause, roughly in second position. Otherwise, you can rearrange phrases much more freely than in English.

What is the difference between potpuno, sasvim, and skroz in this context?

All three can mean completely, but there are register differences:

potpuno – neutral, standard, works in both spoken and written language.
sasvim – also standard; in many contexts it is close in meaning to potpuno.
skroz – more colloquial, informal speech.

In your sentence, you could say:

potpuno sam ispraznio bateriju – neutral, standard
sasvim sam ispraznio bateriju – also fine, maybe a bit more emphatic style-wise
skroz sam ispraznio bateriju – sounds more casual, colloquial

All are understandable; potpuno is the safest “textbook” choice.

Can I omit potpuno and still keep the same idea?

Yes. You can say:

Nakon dugog videopoziva ispraznio sam bateriju na tabletu.

Even without potpuno, it usually implies that the battery ended up empty, because isprazniti bateriju by default suggests draining it fully.

Adding potpuno just makes the idea of completely explicit and a bit more emphatic.