Running 4A on a DC motor using an Arduino Motor Shield R3

Hey guys,

as the project rolls on we are sort of making it all work.. somehow.

we are running 12v from batteries into the arduino motor shield. then controlling the 2 dc motors is all good- one in channel a and one in channel b.

but i know that the motor shield only gives max 2A per channel. the motor in channel b is a 12v dc motor and we need more torque out of it but still want to run it through arduino.

the question now arises:

is it possible to hook up another battery in between the arduino motor shield and the dc motor ?

aka- have 12v into the arduino to power it. then have seperate battery in between the motor shield and the dc motor ?

i read that it is possible to hook up an external power source for a servo- do you just hook up the battery to the power cable and ground to ground ??

thank you