I'd like to have a 12v battery pack, using throwaway batteries, for
extended field ops with my Yaesu VX-5R HT. I want to be able to
operate without having a genny on hand, and throway cells of a
standardized type allow me to say to Logistics "Uh, go gimme a raft of
them thar D cells", simplifying my life in the process.

Anyone done this with either four pairs of D cells or a pair of 6v
lantern batteries?

IIRC, IEC-type D-cells are normally designed to deliver 200mA, whereas
the lantern batteries are designed to deliver 300 mA. Is that correct?

Many thanks for your helpful and on-topic advice.