Kuryakyn LED battery gauge (PN: 4218)
Got this off of Ebay that had the best pricing. Easy installl, and a nice little unit that fits in hard to place location.
Can be seen in daylight very easy.
(http://fjowners.com/gallery/3/1388_15_07_12_11_37_04.jpeg)
(http://fjowners.com/gallery/3/1388_15_07_12_11_38_10.jpeg)