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2007 BMW 530d E61 LCI I had a new battery installed last year.
Several error messages appeared last week while driving, prompting me to consult a local professional, suspecting the voltage regulator might be defective.

They reported that everything was satisfactory, with the battery at 98% capacity.
Attempted to utilise it a week later, but the key fob failed to unlock the vehicle.
Utilised the skeleton key to unlock the driver's door, lifted the hood, and assessed the battery voltage, which registered at 2.26 volts.
No signs of life; no display, nothing.
No other doors would open; I had to enter through the rear to access the trunk and reach the battery.
Which was astonishingly diminished.
I purchased a new battery today, thinking it will resolve the issue. However, may there be other factors contributing to this significant discharge, or is it merely a defective battery?

Have you assessed the voltage at the battery terminals to eliminate the possibility of a faulty connection? To the best of my recollection, E6x models previously experienced corrosion at the transfer places where the positive cable penetrated the boot floor. A recall was issued for it in the past.

Prior to determining whether the issue lies with a defective battery or an excessive drain, it is essential to do a parasitic drain test utilising a new battery and an ammeter.

The voltage measured 2.26 volts across the battery terminals, consistent with the reading under the bonnet.
My charger fails to detect the low voltage, preventing me from recharging the battery.

Agreement on the parasitic drain issue.

What was the make of the battery installed in it?

I would consider charging it and inspecting the car while it is operational; frequently, when I have observed a healthy battery deplete rapidly without usage, it has been attributed to a short circuit, and if that is the case, one would not want to jeopardise a new battery.

The manufacturer of the battery is Yuasa.

It is quite improbable that a Yuasa battery has malfunctioned within such a brief period.

I am currently in a dilemma on whether to install the new battery or to postpone the decision until I can schedule tests.
It will still be necessary to adjust it for fitting into the garage.
What an inconvenience!

Recharge the obsolete device.

A Yuasa battery malfunctioned within three months.
This is the first and final vehicle battery of that brand for me; but, years ago, they were the greatest for bicycles.