That sounds like a low number. I use soft ones from Pro Sports, called Contour Power Grips. I do change balls around quite a bit, but I use my spare ball most of all. I change its grips maybe once every 6 months or longer.
Some other thoughts:
Oh, by the way, the thinner the thickness of the grip (that is, the larger your finger. The stock overall diameter of most grips is 31/32". ), the more often you're likely to change the grip because the thinner ones takes less use to squash or compress them. My large one is 25/32" and it is about 1/8" thick.
If you use larger inserts, say, 7/8" or so, the thickness of the grip is going to be fairly thin to start with. You're going to compress them faster than I will.
I also suspect that if you use heavier balls, say 16 lb, to my 15lb and you have very strong hand gripping power/strength, these factors might also lead you to compress your grip quicker than I will.
