Терморегулятор находится на батарее.

Because на here means on in the sense of location, and Russian normally uses the prepositional case after на when talking about where something is.

• dictionary form: батарея
• prepositional singular: на батарее

So:

• батарея = radiator / battery
• на батарее = on the radiator

This is a very common pattern:

• на столе = on the table
• на стене = on the wall
• на батарее = on the radiator

Yes, Russian can often leave it out in everyday speech.

• Терморегулятор на батарее. = The thermostat is on the radiator.
• Терморегулятор находится на батарее. = The thermostat is located on the radiator.

Using находится sounds a bit more explicit or formal, like is located rather than just is.

So the version with находится is perfectly normal, but slightly more descriptive.

Here находится means is located, is situated, or simply is in a physical location.

It comes from the verb находиться, which is the reflexive form of находить in a different meaning pattern. In modern usage, you should mostly learn находиться as a set verb meaning to be located.

In this sentence:

• терморегулятор = subject
• находится = is located
• на батарее = on the radiator

The -ся ending marks the verb as reflexive in form. But in many Russian verbs, especially common ones like находиться, the meaning is not literally reflexive in the English sense.

So you do not need to interpret it as finds itself here. Just learn:

• находиться = to be located
• находится = is located

This is one of many Russian verbs where -ся is simply part of the normal dictionary form.

Because the sentence means the thermoregulator is on the radiator, attached to it or positioned on its surface.

Russian uses:

• на for on
• в for in / inside

So:

• на батарее = on the radiator
• в батарее would mean something like inside the radiator, which is a different idea

Yes, батарея can mean battery, but in everyday Russian it also very commonly means a heating radiator.

So the word has multiple meanings depending on context:

• батарея телефона = phone battery
• батарея в комнате = radiator in the room

In this sentence, because something is physically on it, батарея is very naturally understood as radiator.

It is in the nominative case, because it is the subject of the sentence.

The sentence structure is:

• Терморегулятор — subject, nominative
• находится — verb
• на батарее — prepositional phrase showing location

So терморегулятор is the thing doing the grammatical action of being located.

Yes. Russian word order is more flexible than English word order.

This sentence could appear as:

• Терморегулятор находится на батарее.
• На батарее находится терморегулятор.

Both are grammatically correct. The difference is mostly about focus:

• Терморегулятор находится на батарее. focuses first on the thermoregulator.
• На батарее находится терморегулятор. focuses first on the location.

English usually keeps a more fixed order, but Russian often moves parts around for emphasis.

It is pronounced approximately ba-ta-RYE-ye.

The stress is on the last е́ sound of the stem:

• батаре́я = ba-ta-RYE-ya
• на батаре́е = na ba-ta-RYE-ye

So the ending -ее does not sound like English ee alone; it is more like two vowel elements, roughly -ye after the stressed syllable.

Yes. Терморегулятор is masculine because it ends in a consonant in its dictionary form, which is a very common pattern for masculine nouns in Russian.

That is why the verb is singular and agrees with a singular subject, though in the present tense Russian verbs do not show gender:

• терморегулятор = masculine singular noun
• находится = 3rd person singular

You would mainly see the masculine gender more clearly in the past tense:

• Терморегулятор находился на батарее. = The thermoregulator was on the radiator.

Normally, no. In present-tense Russian, есть is usually not used as a plain equivalent of English is in sentences like this.

Russian typically says either:

• Терморегулятор на батарее.
• Терморегулятор находится на батарее.

Using есть here would sound unnatural for standard basic location. In modern Russian, есть more often means there is / exists / available rather than just functioning as a simple present-tense is.