Dead batteries again

Another quick easy test i usually do is have someone turn the headlights on while you watch them. Are they bright and then get real ddim and go out. Do they not come on at all? If they come on bright and seem to only dim slightly have a helper try to start the vehicle while you are watching the lighrts. I they immedateley go out and you hear the click then not only clean the Battery cables but find the ground to the body or engine and take it loose and clean it really good. I had my ground got coated and it wouldn't let the Ground cable make good contact. Lights were bright until I tried to start it and then went out as I tried to crank it!! Only a thought I had. Hope you find the issue soon, I know that can drive you nuts!!!
Dad