Something like this?
http://www.andymark.com/product-p/am-0995.htm
If it is something like this, I think it would be hard for you to drum up customers, as this is already being sold and many teams like it; unless what you make is functionally similar and cheaper.
Will you test at load? Because, as I understand, voltage without load isn't enough to know if a battery is charged or not.
EDIT: guy above me basically hit the nail on the head.