Lots of folks are into electric motorized tadpole trikes. One option is the Ridekick trailer pulled behind a trike. It has the battery and motor on board and can push the trike along.
http://electricbikereview.com/ridekick/power-trailer/
Most definitely anyone considering one of these units would do well to read the review as the list of pros and cons is interesting.
Here is a YouTube video of this product and here is the description of the video: The Ridekick is a bicycle trailer with built in motor that pushes the rider like an electric bike. It’s easy to connect and disconnect, learn more in this review and interview with the CEO of Ridekick.
The approximate price is $700. The top speed is about 19 mph motor power only. The standard lead acid battery is good for about 12 miles (45 minutes) of riding while the lithium battery is good for about 25 miles (2 hours). The lithium battery version is about $1359. The unit weighs in at about 43 pounds with lead acid battery and 38 pounds for the lithium battery version. Battery replacement is $125 for the lead acid and $795 for the lithium battery. Charge time for the batteries is 5 hours for the lead acid and 3.3 hours for the lithium. The batteries can be recharged an estimated 400 times for the lead acid or 1,500 times for the lithium before degradation.
The trailer has a cargo volume of 41.8 Liters and can haul up to 75 pounds of cargo.
I am sure it isn’t everybody’s cup of tea, but some may like it. For sure you need to know the rules where you are riding. On our local trails here where I am at motorized vehicles are not allowed. It is lesser money than most electrice trikes. Extra batteries could be purchased and extend the time and distance the trike could be ridden. Of course, pedaling will also increase the time and distance. And pedaling is the whole purpose … exercise!
tadpole trikes … bring out the kid in ya’ 🙂
A FREE GIFT awaits you!
[Update] Ridekick trailers are sold out through the end of 2014. The company is refining the product and working on the next iteration. All existing warranties are being honored and the company is still in business.
Tadpole Rider 
Ahoy There, Steve, I like your blogs, put me on your list. dmbrown@urcad.org
Hi Dan, Thanks for your kind words. Hey, I know of know way from my end to add you to a list as a follower of this blog. There are buttons to click on to do that. One of them should be at the very top of the blog and the other one near the bottom of the side menu. Just click on it and add your email address when asked for it. It is easy to do. STEVE