Learn Hardcore Russian: Дома я ставлю планшет на зарядку, чтобы он не разрядился ночью. - At home I put the tablet on charge so it doesn’t run out of battery at night.

Дома means at home. It’s used as an adverb (a fixed form from дом), so you don’t treat it like a normal case ending you can freely change in this sentence. It answers where? → at home.

Why is the word order Дома я ставлю... and not Я ставлю... дома?

Both are possible, but the focus changes:

Дома я ставлю... = At home, I do this (contrasts with elsewhere).
Я ставлю... дома = I do this, at home (adds the location later, often less contrastive).

Russian word order is flexible; placing Дома first highlights the setting.

Why use ставлю (from ставить) with a tablet? Could I use кладу?

Ставлю literally means I set/stand (something up)—often used when you put an object in a stable position, like on a desk or onto a charger stand/dock.

Кладу = I lay/put down (more like placing it flat).

With devices, ставлю на зарядку is a very common everyday collocation meaning I put it on charge (regardless of whether it’s literally standing).

What case is планшет, and why?

Планшет is accusative singular (direct object): I put (what?) the tablet. For inanimate masculine nouns like планшет, nominative and accusative look the same: планшет.

What does на зарядку mean literally, and why is it на + accusative?

На зарядку is a set phrase meaning onto charge / to charge (it).

Grammar-wise:

на
- accusative often indicates movement to a destination (put onto / place onto):
  - ставлю на зарядку = I put it onto the charger/into charging.

Compare:

на зарядке (prepositional) = on charge / charging already
Example: Планшет на зарядке = The tablet is charging.

Why is there a comma before чтобы?

Because чтобы он не разрядился ночью is a subordinate clause of purpose (so that...). Russian normally separates such clauses with a comma:

..., чтобы ...

How does чтобы work here?

Чтобы introduces a purpose/goal: in order that / so that. The structure is basically:

Main action: Дома я ставлю планшет на зарядку
Purpose: чтобы он не разрядился ночью = so that it doesn’t run out of battery at night

Why is он used? Can it be omitted?

Он = it (tablet is masculine: планшет → он).

It’s often included to make the subject of the subordinate clause explicit. In casual speech it can sometimes be omitted if it’s obvious, but keeping он is very normal and clear:

..., чтобы (он) не разрядился ночью.

Why is the verb разрядился in the past tense if the meaning is about the future (night)?

After чтобы, Russian commonly uses a past-tense form to express a desired/undesired result (a kind of subjunctive-like pattern), even when it refers to the future:

чтобы он не разрядился = so that it won’t end up discharged

You may also see:

чтобы он не разрядился (very common, result-focused)
чтобы он не разряжался (process-focused: so that it wouldn’t be discharging)

Why perfective разрядился and not imperfective разряжался?

Aspect changes what you’re preventing:

не разрядился (perfective) = don’t let it end up discharged / don’t let it run down completely (focus on the result).
не разряжался (imperfective) = don’t let it be discharging (focus on the process, less common here).

With batteries, the usual worry is the final result by morning, so perfective разрядился fits well.

What is ночью grammatically, and why not в ночь / в ночи?

Ночью is a standard adverbial form meaning at night / during the night (historically instrumental). It’s the most natural way to say this in Russian.

в ночь usually means on the night of... (more like “that particular night”, often with context).
в ночи is uncommon/poetic and not the normal everyday choice here.