Battery level sensor accuracy?
 

I just replaced my battery in my 2004 with an AGM. Used a obdeleven tool and recoded the battery to the vehicle. Within a week I'm back down to 70%. I'm running about a 14.7 voltage while running and the battery test good. How accurate are the battery level sensors in our cars?

Terrible in my experience is the short version, and the display tends to read "after the fact" in terms of providing any meaningful heads' up.

BUT, said another way, from my own experience anything less than 100% and not tied to something obvious--long tunes session post shut down, VCDS work with ignition on for a while, etc.--are indeed a warning something may be up. Given the data you have, would suggest looking for discharge/drain issue. For the all in vogue subject on the board these days, for example any chance your suspension compressor is working overtime? Put in jack mode while car is parked if any suspicions--both on battery and on level. Variety of other scenarios as these age too--alarm horn that fries out internally, various MMI modules that don't go to sleep, comfort door handles, and others.

I haven't noticed my compressor or any other components staying on. I drive the car everyday and would assume that the battery would charge while driving.

Yes, but.. To my point, I found the display sort of reads about what happened in the PAST--like the VCDS work that shows up at the start of the NEXT drive as a lower %. And voltage while driving is tending to indicate charging, while display (being somewhat in arrears) is maybe saying it was starting from a deficit. Again, starting point for me is if display says ANYTHING but 100%, in my 100K plus miles it meant one of owner stupidity (me) leaving lights on, the neighbor kid with my remote running tunes and unlocking car about 50 times, a battery crapping out, or some kind of post shut down current bleed (which I never had).

Feel free to ignore the advice, but some of the pointers are easy. And, do you really know if your compressor ran 4 hours after you left the car to true the level back up without you realizing given leaks on D3s are basically a "when not if" ? Folks who have found the horn, door handle or various sound system/MMI issues often had no direct tip off either besides an apparent current drain. A few others had a faulty replacement battery that got warrrantied. You might also look at whether your battery recoding really stuck.