To see if you have a problem when cranking just put neg voltmeter lead on driver side NEG batt post, not terminal, and pos voltmeter lead on pass side NEG batt post and have helper crank 5 seconds or so. Will read 0 if not cranking (and nothing turned on), unless something very wrong, and should be less than 0.05v cranking (way less is better). Digital vm not very useful for this, use old style moving pointer like Simpson 260. Switch and do both pos posts which will show more voltage due to cable setup. Voltage divided by lead resistance and connections equals current imbalance while cranking. For more accurate test, make both neg leads same length and clean terminals. This is one of the battery killers in our trucks. I will try this after finishing reinstalling second battery (now in Bertha).