Thanks Tony, Paul, and Al for the responses and excellent suggestions.
I have returned the malfunctioning grip to the seller-he had a 14 day return policy-and obtained another one from another seller. The second one works perfectly. Both are original Nikon products and I am using Nikon batteries.
I can see how the on/off switch on the grip could eventually fail with frequent use over time, and I will keep the contacts clean to improve performance.
The grip has been invaluable for using the camera in "portrait" mode while shooting indoor basketball recently.
Now if I can improve my techniques to fully utilize the capabilities of my equipment, I will be in good shape!