Low battery will cause flaky stuff and problems, "INTRODUCTION" and "AFTERMARKET BATTERY" has nothing to do with it and will not cause electronic problems.
At the end of the day if one is cheap a$$ and practical like me, they will just throw the biggest "AFTERMARKET" battery that will fit in there and replace it at the first sing of decay. In California that is, in a colder climates i will replace it before the second winter and call it a day. $200 for 1.5-2 years for a battery is nothing in the great scheme of things owning E70 X5 in any form.

Given the sensitivity of charging an AGM battery the wrong amount, and that the BMW is intelligent enough to charge a battery differently based on the amp-hours of the battery, why not take advantage of this feature? Assuming one has the proper equipment, coding a battery takes less than a minute.

^^^ I absolutely agree. But if someone has to pay $400 to get the battery registered, or even $200, that is outrage. Like everything else, BMW made it for a reason, but it is misinformation that something in the car will fail if replacement battery is not registered.
And one more thing. If the car is driven on a short trips and the battery charge stays on the low side the module will try to charge it as much as possible for the short intervals driven, which will lead to a short battery life regardless of everything else. I like the ISTA future showing the system voltage at all times and I have figured many problems because of that display. Most modern BMWs will have 14.2-14.8V with engine running, but I have seen many with as high as 15.5V for extended driving periods.

FWIW I changed my troublesome 5 year old 90AH AGM battery for a quality 110AH standard lead acid. Reprogrammed battery type and registered with BMWhat tool. All works fine with much improved cold cranking. Total cost under £150

That's crazy. It takes about 10 minutes to change a battery in an E70, including coding. If a shop charges any more than 1/2 hour labor for all that, it's time to find a new shop.

Keep in mind that it's really a good idea to charge your new battery before install, (with a charger designed for AGM batteries if that's what you're installing). Best is to use a slow charge method or "trickle" charge, so you need to count on that taking at least several hours.

OT, but aside from 14.7v for AGM, that is what have not FULLY READ UP ON why the car needs to be registered, etc for AGM batteries, and the way BMW has their registration/charging profile setup for them

I posted this link here in the OT Lounge Forum
http://independentmotorcars.com/2010...tons-of-dough/

Great write-up on situation that repeats time and time again. Connecting/disconnecting the battery with the key in the ignition is a bad practice and may, or may not, damage the CAS. In a modern car every module is powered-up permanently (terminal 30) regardless if ignition is ON or OFF(terminal 15). Real damage to the modules happens when the voltage drops under 8 volts for a prolonged periods(battery going low and still connected to the car). What happens is that the volatile memory(RAM) and non-volatile memory (so called FLASH memory) often gets corrupt from the undervoltage and the MCU executes wrong instructions. Here is your explanation why many times disconnecting the battery may fix some strange behaviour or bring back a "dead" module. It is the same thing as if one reboots their laptop or desktop. If the FLASH is intact the module will load the correct data and will work as new again. Sometimes reprogramming will fix a corrupt data, but if the boot sector is damaged usually the module is considered "dead" and unrepairable. Of course we have ways even around that by reprogramming it directly on the lowest level- MCU and/or FLASH instead thru the diagnostic ports.
Just to clarify my position on all the modern electronic stuff. Respect the car, but dont be scared of it. Being afraid and looking at the electronic systems as "black box" gives more power to the dealers and people trying to take advantage of us. Battery is a battery and proper maintenance, operation and instalation is valid for every car, old or modern. Even if everything is done by the book modules get damaged too and there is nothing we can do.

What do they mean by 'sonically tested' ???

Bawareca -

Can you shed some more details per the article I linked.
I mean 14 volts aside, why does the registration etc, need to be acquired. CCA, etc. That's purely for the role in starting the engine....why would the vehicle know that in order to charge the battery. Isn't it's role it to just charge it to 14.7, aka, AGM voltage specs...

You don't actually put in the CCA when you code the battery. You use your scan tool to tell the car you are changing battery, and if you are changing the battery type, (ie. AGM vs Acid), and if you are putting in a battery with a change in Amp Hrs. (ie 92ah vs. 90ah). The scan tool will register the date of the battery change in the car's memory. From that point, I'm not sure if the scan tool evaluates the new battery, or the car evaluates the new battery, (my guess is that it's the car,) but the process happens automatically, you don't need to enter the data of the new battery, just whether it's different or the same. And you're done....1 minute or less.

But the car's computer controls the charging process of the alternator in a way that is specific to the type and power of the battery, along with its age.