Wal-Mart $15

I found a very similar item at Wal-Mart for about $15.

I've used in the cigarette lighter of my truck and verified it's readings with a different battery tester.

I plan to use it on my bike in a similar way as you plan to.

 

I got one a few weeks ago and was pleased with the readings and the simplicity. However, it isn't a very sturdy item and it broke (?) Still works, but the plastic collar is dead meat.
If I got another one I would adjust it to my liking and glue or gorrila tape it to that adjustment.

Rick