Here is how I do it. Watch from 0:47 - 1:27. While not RailPro, the setup would be the same.
You might want to re-consider your battery choice unless you are space constrained. I used the Train-09 (14.8V 3.5Ah). I can run my O Gauge train for over three hours straight.
.68 Ah will not run very long IMHO. You can also get MTO batts at
https://gscaleinstallations.net/14-8-v-batteries-1 for a better price.
My first Railpro system is due to arrive Tuesday. I'm very excited.
Have Fun!
Ron