expected normal voltage drop from load?

Thanks for the responses. I did suspect that the cold temps and higher resistance of 6V might be culprits for what I observed. The last time I did this experiment I do think I was still running 2x12V marine batteries. So that could explain me not remembering any low voltage issues.

I didn't take any SG readings prior to experiment due to darkness and laziness, nor afterwards. 12"+ new snow over night, I'm not going to unbury anything anytime soon to take readings!