Зимой аккумулятор в машине разряжается быстрее, поэтому папа проверяет его заранее.

In Russian, seasons can be used in the instrumental without a preposition to mean during that season.

So:

• зима = winter
• зимой = in winter / during winter

This is a very common time expression, similar to:

• летом = in summer
• осенью = in autumn
• весной = in spring

You can also say в зимнее время or similar longer phrases, but зимой is the normal natural way.

В машине means in the car, and машине is in the prepositional case because в is being used for location.

• машина = car
• в машине = in the car

Compare:

• в машине = inside the car
• на машине = by car / using a car as transport

So in this sentence, в машине is about where the battery is located, not how someone travels.

Because аккумулятор is in the nominative case, and the verb разряжается agrees with it as the thing that is doing or experiencing the action.

So the structure is:

• аккумулятор = subject
• разряжается = goes flat / discharges

Russian does not rely as heavily on word order as English does, so case is a major clue. Here, аккумулятор is the thing that becomes discharged.

The verb разряжаться means to become discharged / to run down / to go flat.

The -ся form is important here because the battery is not actively discharging something else; rather, it itself is becoming discharged.

Compare:

• разряжать = to discharge something
• разряжаться = to become discharged

So:

• Я разряжаю аккумулятор = I am discharging the battery
• Аккумулятор разряжается = The battery is getting discharged / going flat

This is a very common pattern in Russian: a non--ся verb can be transitive, while the -ся version can describe something happening to the subject.

Быстрее is the comparative form of быстро:

• быстро = quickly
• быстрее = more quickly / faster

In Russian, you often do not need чем (than) if the comparison is general and the second part is understood.

So:

• разряжается быстрее = discharges faster / goes flat faster

If you wanted to state the full comparison, you could say something like:

• ...быстрее, чем летом = faster than in summer

But in your sentence, the idea is simply that in winter it happens faster than usual, so быстрее by itself is enough.

Поэтому means therefore, so, or that’s why.

It links the second clause as a result of the first one:

• In winter the battery goes flat faster,
• therefore / so Dad checks it in advance.

It is very common in Russian for showing cause and result.

Compare:

• потому что = because
• поэтому = therefore / so

So:

• ...разряжается быстрее, поэтому... = ...discharges faster, so...

Russian often leaves out possessives like мой (my) when the meaning is obvious from context, especially with family members.

So:

• папа can naturally mean Dad or my dad, depending on context.

This is very common in everyday speech. English usually needs my dad, but Russian often does not.

Also, папа is informal and natural in family-style speech. A more formal word would be отец.

Проверяет is the imperfective present, and here it describes a habitual / regular action.

The idea is not one single completed future check, but something Dad does as a precaution whenever this situation applies.

• проверяет = checks / is checking / checks regularly
• проверит = will check (one completed future action)

So the sentence suggests a general pattern:

• In winter, the battery discharges faster, so Dad checks it beforehand.

If you wanted a one-time future meaning, Russian would use something like проверит.

Его refers to аккумулятор.

Here it means it and is in the accusative case because it is the direct object of проверяет:

• проверяет что? — его
• checks what? — it

A useful point: его can also mean him, so context matters. In this sentence, because аккумулятор is masculine singular, его clearly refers back to the battery.

Заранее means in advance, before it is needed, or ahead of time.

That is slightly different from раньше, which usually means earlier or before in a more general sense.

Compare:

• проверить заранее = to check in advance, as preparation
• проверить раньше = to check earlier than something else / earlier than expected

In your sentence, заранее is the best choice because the idea is preventive: Dad checks the battery before a problem happens.

Yes. Russian word order is fairly flexible, and changing it usually changes emphasis, not the basic meaning.

The original sentence is natural and neutral:

• Зимой аккумулятор в машине разряжается быстрее, поэтому папа проверяет его заранее.

But you could also hear variations such as:

• Зимой аккумулятор в машине быстрее разряжается...
• ...поэтому папа заранее проверяет его.
• ...поэтому заранее его проверяет папа.
  This last one is more marked and less neutral.

In general:

• earlier position often gives a word more emphasis or topic status
• later position can make it sound more focused or new

For learners, the original version is a good standard model.