2004 QX56 .. 115K

When my wife starts it .. sometimes it starts right up and other times it acts like a weak battery ... but then she stops and trys again and it fires right up

battery is less than 2 years old
terminals on the battery are clean
voltage on the battery is fine ..
no codes

have been reading about IMDB or something like that but unsure what that is
how to test if it is bad or good?
reads like a relay or something like that ..

anymore info or tips on what to check would be great . I don't want her to get stranded.. I hate when things sometimes work .. I rather it just break in the driveway..

Thanks for the future help

Just looking at the voltage on a battery isn't a good test. Go to any auto parts store and have a load test done on the battery.
The problem with the IPDM was a relay for the ECU. This would not cause the weak battery problem.