InfoLithium battery production date

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Hello!

Few years ago I found a simple guide in the internet how to read production dates for Sony batteries.

Then I forgot the logic in the serial number and now I can't find anything anymore about serial numbers.

Seems like the information has vanished into thin air.

 

Anyone here who can tell when a battery was produced looking from serial number?

 

For example:
My batteries (Sony infolithium W -series) serial numbers: K1FQR 1ER, K2LSK 1ES, K3J5K 1EB

 

Thanks!