This was reviewed in the latest issue of Rider and I thought it was neat, especially if you have Battery tender leads on your battery but don't have a voltage regulator display. Go here and search for Voltage Indicator ---> Deltran Battery Tender
You just plug it into the leads and the voltage is displayed on the read-out. It also has red, yellow, and green lights which indicate battery condition.
Listed for $16.95 but less expensive doing a search.