Pos>Pos, Neg>Neg is called 'in parallel'. It's the way you should 'jump' start cars. It will maintain the voltage at 12v no matter how many batteries you connect this way 'in parallel'.
If you connect Batt 1 Neg> Batt 2 Pos, then across the other terminals, you will have the sum of the voltages of each battery. Starts to become a very powerful effect. Therefore I would expect the current (ie amps) to be the sum of each battery.
School physics was back in the 60s!