Assuming you are still using 12 volt batteries which is what Newell uses, the negative cable is hooked to the negative terminal on battery 1, a jumper cable goes from the negative terminal on battery 1 to the negative terminal on battery 2, another jumper cable goes from the positive terminal on battery 1 to the positive terminal on battery 2. If only two batteries are in parallel, the positive cable then is connected to the positive terminal on battery two.
diagram from solarseller.com
In short all the negative leads are tied together, all the positive leads are tied together with the negative cable tied to the negative terminal of the battery at one end of the battery bank the the positive cable tied to the positive terminal of the battery at the furthest away.
My coach uses two batteries in the chassis or starting circuit and two in the coach or house circuit. These batteries are isolated from each other unless the battery merge switch on the dash is activated.
If your batteries are going deal overnight, either one of the batteries is reversed in polarity or you have an extremely large draw on the batteries such as a short.
Give us a little more information on your hookup and we will try to help out.
Remember NEVER use series wiring unless you are dealing with 6 volt batteries OR in the case (a manufacturer of conversion bus shells) where 24 volts is used. I have never seen a Newell that was using 24 volts.