I've had noticed this also. The alternator does get to 14+ V but only when necessary.
The reality is that any car that has a current sensor will control the the alternator's output only on demand.
This means what ever old practices you have in the electronics department will need some revamping. Just like the Octopus multi ground kit was, in theory it looked like a possibility until you missed the part of the current sensor and how ALL grounding wires have to go through this for the car to be able to control the alt's output.

Having your alternator charge at 14v all the time is unnecessary.
It turns into it's own heat source
It decreases it's overall life of the unit
It creates additional and unnecessary drag lowering your efficiency

I can guarantee that with the correct and maintained battery + 10 + miles of driving will fix any issues you might have.

 

I'm having this issue on my 08 for years, i have to coastally jump my car after it seats for more than 2 days. it literally drops to 11.2 v and lower. do we have a solution to this? my next step is disconnecting the oem radio since i hear is a common problem.

 

I don't know if it's a common problem because people that don't have a battery drain are not going to search for battery drain and will therefore not find this or other related topic and therefore will not post any reactions.
But when your car won't start after 2 days there is a problem because that is not normal.
I would start with measuring your charging voltage and check if your battery is ok. If you are 100% sure these are ok, then measure the current when the car is in sleep mode (this takes about 20 minutes). Then use a DC camp measuring tool to measure the current, this should be around 0,09 A. I used this tool, it's easy to use because you can clamp it around the negative cable on the battery.
If it's above the 0,09A then you have a battery drain. Then use video to find the fuse group which is causing the drain.

 

I too have an 08 G37 and the battery has always drained after more than 2 days of sitting. Even when I bought it from the dealership they had to jump it off. I don’t think it’s the OE radio. I have an aftermarket unit and it still drains.