I had the same type of problem winter before last... I bought a new battery, and nothing. Got a new starter. Fixed the issue. The old starter plus glowplugs were pulling the battery waay down.

 

I will agree with what your saying ,but if tested and retested the battaries,charging,and glow plug system.Unless the Fluke meter and my scanner are lieing I don't think this is the issue.Been WRong before,still think it is a fuel issue or idm problem.I HATE throwing parts at things without knowing....anyone have any injectors to donateMaybe a IDM,Keep the thoughts coming I DO appreciate them
PS was letting it idle this morn to move it and actually seen some black smoke from the tailpipe.Maybe the seafoam is working on the injectors