How do I tell the age of my car battery?

[LeoSayer]

It's a Varta with these codes stamped on top.... G4B5922120743 510126 29B

Is it G4 for July 2004?

Or 5101 for 51st week of 2001?

Or something else?

[LeoSayer]

No coloured dot unfortunately. Thanks for the pdf but no real match.

I know it's at least 5 years old. It's currently out of the car and on the trickle charger as I accidently discharged it yesterday.

Just wondering if it's worth persevering with it.