I use the same technique as 123 300D driver. If your battery can't heat up the glowplugs for 10 sec either there's a short in the glowplug system or your battery is marginal. The glowplug system is only a few components and should be pretty straightforward to get in shape.
My car has started as cold as 8 deg F without a block heater, and I triple glowed the thing and botched at least one cranking attempt by stopping cranking before she fired. It did take about 20 sec (seemingly) of cold cranking for the engine to keep running. I think my Optima battery (red-top) helped turn the sucker over. The winter before, I did kill a perfectly good Interstate battery trying to start a not-plugged in 77 300D in 20 degree weather. And I know that battery was good, because after charging it, I took it to National Auto, and it delivered 200(!) amperes and the voltage stayed at 11 volts.
Also, I see you're using 20W50. That may be too thick. Is this your first winter? Not sure where you're at, but I use 15W40 Shell Rotella T or Chevron Delo 400 here in eastern Pennsylvania. Even that is like molasses in cold weather, but I can't find a thinner CG-4 rated oil for sale around here, and nobody seems eager to mail-order oil (if it's even legal).
Lehigh Valley PA USA
73 Olds 88, 72 MB 280SE, 78 Datsun 280Z, 71 T-Bird, 72 Olds 88, 83 Nissan Sentra, 85 Sentra, 73 230.6, 91 Integra, 83 300SD, 91 Volvo 940GLE wagon, 84 300SD, 95 Subaru Legacy L wagon, 02 Mountaineer, 91 300TE, 08 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon all gone... currently
2007 Honda Odyssey Touring, 2011 Honda Odyssey Touring