Although it could refer to the cooling system (radiator), I'm looking right at you, Mr. Battery.
Autumn has hit Chicago and day time temperatures now vary between the upper 40s and low 70s. When it's toward the lower end of that scale, any issues you might have, with the battery, will manifest themselves quickly. VTRs are power hogs on start-up. If your battery is weak, you're going to discover that fact post-haste.
I discovered that the electrolyte had fallen to low levels by trying to start the VTR on a chilly day (~48º F - a week or so ago). A couple of cranks and it was obvious that the motor wasn't going to start using the starter motor. I am fortunate enough to park in a parking garage. All I had to do, to get the motor running, was to walk the bike up the ramp, snick it into second gear and coast down, popping the clutch along the way. The engine fired right up and I was on my way.
The following day (a Saturday), I took a closer look at the battery to see if it really was low on electrolyte or if it was no longer viable. Sure enough, all of the cells were low (below the top of the plates). Fortunately, I had some distilled water handy. Using a small funnel (a syringe, without needle, will work, too), I topped off each cell. It was very helpful to use a flashlight to illuminate the battery from behind. That makes seeing the electrolyte level very easy. Fill each cell to the level indicator, as printed on the battery side, and then put the battery on a charger.
Now, if your battery is a sealed unit, you obviously cannot add water to it. In this case, it's best to have it load tested (to see if it's still good). Any chain auto parts store (Auto Zone) will be able to load test it for you.
Should you need a new battery on short notice, I found that Batteries Plus stocks a battery that will fit the VTR (at least my local Batteries Plus store did). They do have to charge it so if you need one, be sure to give them some advance notice.
While the battery is out, take this opportunity to clean the terminals (baking soda & water works well here) on both the battery and cables. You can also clean the battery box, if necessary, too. Corrosion will limit the electrical system's ability to charge the battery.
Use distilled water only. Tap water has minerals in it that can cause the battery to become less efficient.
I have one of those Black & Decker Snake Lights. It makes illuminating the battery, from behind, a hands-free chore. If you don't have something similar, enlist the help of a friend or family member.
You will need a way to meter the distilled water as you fill the battery. Overfilling can cause problems. Use a small funnel, plastic syringe or turkey baster to ensure that only the proper amount of distilled water enters each cell. If you over fill, you can't simply dump the excess out. That's acid in there!