Again, I know it has to have a complete circuit, so I'd appreciate it if that phrase was left out of any and all replies
d'oh. Okay, I guess my question is now "why isn't the + from battery A to the - of battery B a complete circuit?"
Because there isn't a complete path between battery A and B for current to flow.
A complete circuit would also require a conductive path from -A to +B. It's the same reason you can't just wire from the +A to one lead of a lamp and expect the lamp to conduct current.
QuoteBecause there isn't a complete path between battery A and B for current to flow.Precisely the answer I was trying to prevent with my original wording So is it a hardware limitation or something else? I'm really hoping it's not simply "that's just the way it is"
connecting all the grounds together will not be bad at all and will in fact be necessary to measure voltage differences between each unit?