Ahelyett, hogy az elemeket zsákba tennénk, a gyűjtőpontra visszük.

It is a very common Hungarian expression meaning instead of ...ing or rather than ....

Structure:

• ahelyett = instead of that / rather than that
• hogy = that

So the pattern Ahelyett, hogy + clause introduces the action that is not done, and the main clause gives the action that is done.

In this sentence:

• Ahelyett, hogy az elemeket zsákba tennénk = instead of putting the batteries in a bag
• a gyűjtőpontra visszük = we take them to the collection point

After Ahelyett, hogy, Hungarian very often uses the conditional.

So:

• tennénk = we would put
• not tesszük = we put

This is the normal idiomatic pattern. It presents the first action as the rejected or unreal alternative:

• Ahelyett, hogy tanulnál, tévét nézel.
  Instead of studying, you watch TV.

So in your sentence, zsákba tennénk literally means we would put [them] in a bag, but in natural English it is best translated simply as putting them in a bag after instead of.

Yes, elem can mean element, but in everyday Hungarian it also very commonly means battery, especially a small household battery.

In this context, elemeket almost certainly means batteries.

A few useful related words:

• elem = battery
• ceruzaelem = AA/AAA-type battery
• akkumulátor = rechargeable battery / аккумулятор-type battery

So this sentence is about recycling or proper disposal of batteries.

The ending -et marks the accusative, which is the direct object.

Breakdown:

• elem = battery
• elemek = batteries
• elemeket = batteries (as the object)

So az elemeket means the batteries as the thing being acted on.

It is the object of both actions in the sentence:

• we do not put the batteries in a bag
• we take the batteries to the collection point

Hungarian often marks the object clearly with an ending, where English relies mostly on word order.

Hungarian uses the definite article more often than English in many situations.

Here az elemeket means the batteries, referring to the batteries under discussion. Even if English might say something more general like Instead of putting batteries in a bag..., Hungarian very naturally uses the article when the items are understood from context.

So:

• elemeket = batteries
• az elemeket = the batteries

Both are possible in some contexts, but az elemeket sounds very natural here.

zsák means bag or sack.

The ending -ba / -be means into.

So:

• zsák = bag
• zsákba = into a bag

This is the normal form used with verbs of putting:

• zsákba tenni = to put into a bag

There is no article here because it means into a bag in a general sense, not into the bag. If it were a specific bag, you could say a zsákba.

gyűjtőpont means collection point or drop-off point.

The ending -ra / -re often means movement to a surface, point, destination, or target. With places like this, Hungarian often uses -ra/-re where English simply uses to.

So:

• gyűjtőpontra = to the collection point

Why not the others?

• -ba/-be would suggest movement into something enclosed
• -hoz/-hez/-höz means to/toward something, often more like up to or to the vicinity of

Here -ra is the natural choice.

Here visszük is the normal present-tense form of the verb visz = take / carry.

This is confusing because the form looks like it contains vissza (back), but in this sentence it does not necessarily mean back. It is just how visz is conjugated.

Useful forms:

• viszem = I take it
• viszed = you take it
• viszi = he/she takes it
• visszük = we take it/them

So in this sentence, visszük simply means we take [them].

Because Hungarian has definite and indefinite verb conjugation.

Here the object is definite:

• az elemeket = the batteries

So the verb must use the definite form:

• visszük = we take it/them

Compare:

• viszünk elemeket = we take batteries / some batteries
• visszük az elemeket = we take the batteries

So visszük is required because the sentence has a definite object.

Because Hungarian, like English, can leave the object understood when it is already clear.

The full repeated version would be understandable:

• Ahelyett, hogy az elemeket zsákba tennénk, az elemeket a gyűjtőpontra visszük.

But that sounds repetitive. It is much more natural to mention the object once and let it carry over:

• Ahelyett, hogy az elemeket zsákba tennénk, a gyűjtőpontra visszük.

English does the same:

• Instead of putting the batteries in a bag, we take them to the collection point.

Hungarian simply leaves the object implied in the second clause.

Yes. The comma is standard here.

Ahelyett, hogy ... introduces a subordinate clause, and Hungarian normally separates that clause from the main clause with a comma:

• Ahelyett, hogy az elemeket zsákba tennénk, a gyűjtőpontra visszük.

So the comma is not optional stylistically here; it is the normal written punctuation.