It's very easy to setup 2 18650 batteres into your rapiro battery box, even without any soldering. See my Setup .
1. Like Image1 : Just put the original black and red shims on top of the battery box

2. Like Image 2 : Just put the other two shims on the bottoms of the battery box (PS :You only need to cut into some gaps to hold those two on the battery box bottom, you will have two more shims left). Done.

you still can change back to the original 5 batteries setup since we don't break any items.