How do I know when a VARTA car battery is produced?

Assuming that the 0466 is a Julian date code which is quite common within production facilities including that in the automotive field. The first three digits represent the day of the year and the fourth digit represents the year.

046 = the 46th day of the year or February 15 and the fourth digit 6 =2016

Of course there are numerous other codes used as well. Here is a link that might help.

http://static1.1.sqspcdn.com/static/f/497536/21977226/1361343377317/Battery+part+numbers+and+date+codes.pdf?token=PimTxag8pZv8mjPonrrkbyorwgo%3D

So, I emailed Johnson Controls as well and they answered me:

Good Morning Ulf, I can confirm your battery was manufactured on Sept 2015.

Kind regards Controls Power Solutions EMEA

So, I was right in my guessing and Johnson Controls (the manufacturer) probably has the same stamps for their batteries produced for VARTA and BOSCH. I followed this guide from an older StacExchange thread: https://mechanics.stackexchange.com/a/35523/40744

The key thing is to know what to look for. Batteries sold in the EU must be permanently marked with a means for manufacturers to identify production batches (if needed to recall a defective batch). This requirement does not extend outside the EU, but as many manufacturers have no idea where batches may end up being sold, most arrange for batteries to include the information either explicitly - often on a label stating clearly the year/month the item left the factory - or in a code which is sometimes buried in a lot of other numbers.

A genuine Bosch silver Battery has a very long number laser etched into the case - such as GBC1110330337 290A 24 Ignore everything on the printed labels. With batteries what matters is the number laser etched or physically melted as a string of numbers/letters into the case. To find the month of manufacture ignore the first three letters (GBC) it is the next 3 numbers which will identify when it left the factory. Then look up the three digit code here - http://aa-boschap-ru.resource.bosch.com/media/commonly_used_media/parts/repairs_and_service/_01072015.pdf

I've just bought a silver dynamic battery and underneath the battery the are 2 imprinted dials with mine pointing at 6 and 19. I assume June 2019.

I have bought Bosch/Varta agm battery (part numbers are identical). It has been made by Clarios in Germany (JCi has sell battery business). Serial number is long digit only string without former three letters in the beginning. Into the top cover has printed 4 letter code (HZTJ) but can't find any hit for decrypting.

Into bottom of plastic shell there are casting codes from the mold. It consist two part 19 - 22 for year and 1-12 months "clock". The shell of my battery has made at feb 2020.