All this talk of lithium-ion batteries made me do a little digging into whether they are actually DG or not. Unfortunately I don't have a DGR book or Technical Instruction manual with me, so most of this is off my head and corroborated off the net, so forgive any errors.
As of 2009, Li-Ion batteries under 100Wh could be carried without a DG cert as excepted quantities (under 10Kg). Those over 160Wh need a DG cert under UN3480 Class 9 (RMD).
So for the excepted quantities class, you could have hundreds of Kgs in an overpack, and it would never appear on a NOTOC, and maybe under a shrinkwrapped pallet where you could not possibly see it. Scary.