Unfortunately the VR system details is not explained well by Nikon so a lot of rumors have been the guidelines in absence of data. There are a few things that are known however such as the sampling rate of the VR servo is 1000hz which means the upper limit of predicted performance is 1/500 sec shutter. From my own tests and background in servos, settling time is faster than the shutter response time so once engaged it will track the camera movement within a few cycles of that sampling rate. The shutter response time is between 50 and 75 ms for modern Nikons enthusiast and pro cameras, which is overkill in settling time allowance. The most misunderstood nature of VR is when it is needed. Most shots do not need it and might suffer if used. It only impacts camera movement, not subject movement, so the shutter speed still needs to be fast enough to freeze subject movement or else any camera vibration will be swamped by subject motion. That means slow shutter shots are still the domain of still life shots, not people, sports, animals etc. If it is really a low shutter speed still life, a tripod will be much more consistent. The 1/500 speed limit is a general one based on the Nyquist frequency of the servo. Any faster is luck if it helps. The fastest speed that it ought to be able to track is 1/500 but expect better consistency at 1/100 or 1/250 than 1/500.
The VR function on newer Nikon's follows AF operation and that is a good thing for higher res cameras. The settled mirror image assists in metering, tracking and VF image steadiness. Many of us requested that change and we got it first in the D800 where it was really needed. The D7100 needs it even more due to its higher pixel density.
For those using the built-in flash, note that VR is disabled during high current drain on the battery such as when the flash capacitor is charging between flash shots. An external flash does not trigger that function so normal frame rates can used as long as the flash can recycle fast enough.
In my shooting, the default setting is AF-off and I turn it on when it will probably make an improvement, otherwise it is more likely to undermine my goal of sharpness. Low light interior shots hand held, of still subjects, like museum exhibits gets VR as a general rule. Flash or wide open shots where bokeh is important, it is off. The quality and smoothness of the bokeh is better without VR. VR is great when needed and used appropriately but it is used too often with marginal results because the conditions for which it was designed for are not present.
For the original question about using VR for wildlife and not wanting to drain the battery, you might not be getting the benefit assumed since by nature, the subject is moving so will require a fast shutter speed, and any subject movement will be more than camera movement. Camera movement is amplified by the length of the lens, for example an unsteady hand will move the camera through a much smaller arc with a 14mm lens than a 300mm lens as traced on the sensor.