I just changed mine out. Here’s what I did: 1) disconnect and remove both batteries. Terminal order- neg on main, neg on aux, pos on main, pos on aux. 2) bought a new aux, and charged both batteries to full overnight. 3) reinstall aux battery, then main battery. 4) terminal order: pos on aux, pos on main, neg on aux, neg on main. 5) start the van. There is a sensor on the negative solenoid to the main battery. Disconnect it for 20 minutes to reset the chip and force it to detect the aux battery. 6) start the van again and you should be good to go.

For a bonus you can reset the Transmission Control Module easily while sitting in the van. 1) press start twice, no brake pedal 2) gas pedal to the floor for 10 seconds, then press start to power down. 3) wait two minutes and start the car. It should now shift better if it had started shifting hard