[Teckno711]

Did a ‘deep dive’ and opened up the battery compartment in the X1, sDrive20i.
Battery is new generation EFB.
Banner brand, made in Germany.
12v, 70Ah, 700A (EN).
120CC, 700CCA (SAE).
Two part numbers ?
S 61 216 991 365
AW 61 216 992 187
701788 - 10AT
Battery post week 06, 2021
Warranty commenced mid May 2021.

It appears EFB batteries are ‘lead acid’ on steroids, for ‘stop start’ systems and utilise smart chargers set to ‘normal’ recharging, not AGM.
Developed to meet Euro 6 issues, cheaper to make and slightly lighter.
VARTA have a good info section with cut-away diagrams of normal, EFB and AGM design.
EFB usually used where there is no recover of braking energy.
That said there appears to be no reason why when replacing an EFB, an AGM could not be substituted ?
VARTA recommends an alternative of 80Ah, 800A AGM 580-901080.
Hope this helps.

[wcs2229]

You might as well go for the 80AH AGM battery. My dealer replaced my failed OEM 80AH AGM with an East Penn 80AH AGM 5 months ago.

Definitely register the new battery when you switch the type over to AGM.