No, there is no battery gauge. You can buy a Ctek battery charger from Amazon and that should help w/ your start ups. They come equipped on higher end car brands. I bought the 7002 model for less than $100, but the price went up. The next model down is the 3300 and sells for @ $55. You can also go to smartercharger.com for more info.
My Z had a gauge, and I just figured the much more expensive GTR had one buried somewhere in the main display, I guess not then, I will just wait for the "idiot light" and I hope it gives me enough warning.