Below I share my experience converting a regular lady bike to an electric trailer equipped bike.
This was intended to transport around 6 bottles of water (5 Liter/1.3 gallon each).
Step 1: The Ideia
I wanted to adapt my mother's bike to allow her to ride her bike easier because her health was impaired. In the end of 2010 to buy an electric bike in Portugal was very expensive. The same applied to lithium batteries. So I started making some sketches using my Alibre CAD software; not well know in Portugal but more than enough for my skills at an affordable price.