Battery testing is whole science and having for years load tester, I added this gizmo to my collection.
https://www.amazon.com/gp/product/B0015PI7A4/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
It seems to be way better and more accurate than load tester. Easier to storage as well.
When coming to energy saving modes, MB is pretty quiet about making whole list, but I would not worry about low voltage issues till you get the battery fixed.
Bare in mind that dirty clamps can cost low voltage and errors.

 

Thanks for the reply.. really just trying to figure out why I'm getting the aux bat malfunction message on the dash. Regardless how I test it it seems that the car itself has determined the battery isn't up to what it needs to be unless there's something else going on. The terminals look pristine but will clean just for yucks. Chances are the whatever algorithm Mercedes has programed into the cars diagnostics is something ridiculous and will never be understood. I was hoping someone else might of had the issue and and could confirm a battery replacement solved the issue (before I drop $135 on a batt) without any special resets or messing around. Also trying to confirm if this error disables distronic and the other goodies that just stopped working.

Figures it's just a month out of warrantee!

 

Your vehicle has 2 batteries starter in engine compartment, aux in trunk. Under warranty, have dealer check it, Xentry (MB diagnostics) quick text should identify fault – battery, coupling relay, etc. Out of warranty, find independent. Battery part # is 0009829308 optional with 0009829608 to comparison shop if need be.

 

Even indy will charge you more for battery testing than the HI-TECH tool I linked.
Sometimes when you use indy a lot, they can do such test as appreciation, but don't count on it.
You have lot of vehicles listed in your profile, so sounds like good battery tester can save you lot or money, not even talking about time spend on forum.
The truth is that we can give you procedure advise, but we can't test it for you.

 

Yes, if the battery voltage isn't correct- it will shut of the accessories. 13V? That's not normal for a battery- 12-3-12.8 volts, maybe your measuring tool is not calibrated well.

With the car running- observe the voltage and make sure you are getting 13.8-14.4 volts. What the aux battery read?

 

Here's a link to a recent thread I started. I think a few of the problems I describe will sound familiar to you. When you get to the end of the thread you'll see the source of all the fuss was the auxiliary battery. I've had no further problems at all since it was replaced under warranty.

http://www.benzworld.org/forums/w212-e-class/2890897-2014-e250-sudden-jolt.html