The BMV comes with a shunt that goes on the negative connection to the battery bank and a positive lead that goes to the positive connection of the bank. Its so easy to hook up, that is all there is to it except to plug the interconnecting cord (supplied) into the meter and into the shunt. You have to make sure that all the negative connections to the battery go through the shunt, you cannot have any negative connections directly to the battery except the one to the shunt. You can keep any older system you have as long as its negative connection is on the load side of the shunt.
The BMV 702 has an additional channel that is programmable. You can use it to measure the voltage of an additional battery or you can use it to read temperature (requires an optional temperature sensor - sold separately)