Learn Hardcore Russian: Пиши сообщение, когда устройство зарядится. - Write the message when the device is charged.

Пиши is the imperfective imperative, which focuses on the ongoing action or general instruction (“be writing the message when…”). The perfective Напиши would stress the completion of a single, one-off action (“finish writing/send the message”). In many contexts both are acceptable, but Пиши sounds more like a general guideline, while Напиши would emphasize “make sure you do it once.”

What case is сообщение in, and why?

Сообщение is in the accusative case as the direct object of пиши. For neuter nouns like сообщение, the nominative and accusative singular forms are identical, so you see сообщение in both cases.

Why is there a comma before когда?

Because когда устройство зарядится is a subordinate clause (a time clause). In Russian, you always separate a main clause and a subordinate clause with a comma, regardless of their order.

Why do we use the perfective зарядится instead of the imperfective заряжаться?

The perfective verb зарядиться describes a single, completed event (“when the charging has finished”). The imperfective заряжаться would refer to the ongoing process (“while it’s charging”) without focusing on its completion. Since you want the action to happen after charging is done, you choose the perfective future зарядится.

Could we use a gerund like зарядившись instead of the subordinate clause?

No, because Russian gerunds (деепричастия) must share the same subject as the main clause. Зарядившись (“having charged”) would imply that you (the one who writes) did the charging, not the device. To talk about the device finishing charging before you write, you need a subordinate clause with когда.

Why is there no subject pronoun ты before пиши?

In Russian, the verb ending already indicates person and number. Пиши is clearly 2nd person singular imperative, so saying ты пиши is redundant and stylistically awkward.

Can we insert оно and say когда оно зарядится?

Yes, that’s grammatically correct: когда оно зарядится. But with inanimate subjects (like устройство), Russian often drops the pronoun because the subject is clear from context.

Could the sentence start with the time clause: Когда устройство зарядится, пиши сообщение?

Absolutely. Когда устройство зарядится, пиши сообщение means the same thing. The comma remains obligatory, and placing the subordinate clause first slightly shifts the emphasis onto the condition.

What about using как только instead of когда?

You can say Пиши сообщение, как только устройство зарядится. Как только (“as soon as”) emphasizes immediacy more than когда, but both are correct for indicating “after the device is charged.”