As mentioned, I would replace the battery, it it does not matter it load tested fine, replace the battery. BUT I also suspect you may have an intermittent charging problem like I ran into. You mention that you had 10.8 Volts reading after driving at one point, this means the battery is likely bad and/or 100% depleted on available power due to a no charging situation.
You need to MONITOR the charging Voltage, while Torque will do this, it requires a lot of work to get connected, I would recommend a wired UltraGauge for $70. You can also use the Hidden OBC Menu to monitor the charging Voltage, but it takes some effort to access this on the OBC.
I do not know about the V8 E53, but I can tell you for a fact that my 4.8l E70 WILL NEVER inform the driver of a charging system problem. Not sure if this is a software or design problem, but you can remove the alternator belt and start the vehicle and get NO indication of a lack of charging! Seems to be a V8 only option from what I have seen. I am not the only one that has run into this issue with the N62 X5 platform, albeit mine is an E70.
I had an intermittent no charging problem on start up that I was nursing along for warmer weather and finally replaced the Voltage regulator which I assumed was the cause of the intermittent no charge problem and this did resolved the problem. If it had not been for my UltraGauge not auto starting or waking up, I would have not known what was going on and how intermittent the no charge problem was. The no charge seemed to be related to colder ambient temperatures. I would start the vehicle and have a no charge condition and I even experimented to find out if the charging start if I continued to drive the vehicle, and found out it would not self correct while driving. I had to pull over and restart the engine to get the charging system to work! I nursed the problem along most of the Winter because I did not fancy changing the Voltage regulator in freezing temps.
A few weeks ago I replaced the Voltage regulator and this seems to have resolved my intermittent no charge on engine start condition. I also decided to replace the battery as well because I did not trust it even though it tested fine on many different expensive testers and I was going to be on a week long trip with the family and it is not worth the price of a battery to cause me headaches.
After pulling the battery, found it was over 4 years old and once the new battery was installed the starting performance and charging stability was far better as well. So I am very happy I replaced my "tested good" battery based on my gut instinct at the end of the day.
At least on the E70 the AWD and transmission will go into Limp mode when the charging Voltage drops too low. On the E70 it actually has a lot of power load shedding that is performed to conserve power for the engine to run, but once things start shutting down, you are already in a pretty bad situation. Ask me know I know! If you read the attached thread you will see what happens.
You may want to consider an UltraGauge as a safety net to monitor the charging Voltage and performance on your vehicle. This IS the only way for me to know if my vehicle is not charging. Would be interesting if you removed the serpentine belt on your V8 E53, if you would get any indication of a no charge situation. I suspect there may be a common denominator with the V8 X5 platforms even though they are very different animals. If your wife is the primary driver, the UltraGauge is a good option because you can set threshold alarms for engine temp, Voltage and other item it can monitor. Additionally this is probably the only "automatic" tools that checks for codes every time the vehicle is started, so you will be informed of Pending codes AUTOMATICALLY!
http://www.xoutpost.com/bmw-sav-foru...tem-issue.html
UltraGauge OBDII Scan tool & Information Center
A more advanced scan tool will not likely give you more insight to this problem. My suggestion is to monitor the charging Voltage closely or just replace the Voltage regulator and battery, this will be far cheaper than AutoEnginuity and will likely be what you have to do at the end of the day anyway.
I think the E53 has the water cooled alternator and I would assume the Voltage regulator is internal to the alternator?? I know at least for the E70 V8's it is pretty common that the Voltage regulators only last about 80k miles, not sure about the E53.
Good luck.