EMX RTC pin is known to consume enough to empty a CR2032 in a year. We are upgrading our design now in order to have better performance in term of computation and also to solve some issues that we have. For now we think to go on with GHI products and G400 seems to be a good candidate.
Can anyone tell me how much the RTC battery Ram pin consumes on a G400D?
I would start with the processor datasheet.
I would … like to have the answer 
Doc from processor can be a good starting point but I do not know what there’s between the processor and the external pin and how its behavior can modify the measure.
This supposes current to be constant and I have no clue about that. Does the current is the same when processor is on or off?
So long as the main input voltage is higher than vbat then no current will be drawn when the processor is running.
Estimation provided by Atmel is 8µA in backup mode for VDDBU. However I don’t know how to fully understand the table on page 1244 and if there’s current provided by VDDBU in other modes I assume that in other modes only VDDcore consumes current.
Just for the sake of information
CR2032 with a capacity of 240mAh at 2.0V will have a lifetime of about 3 years and half.
(EMX was 1 year and 4 months)