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