Until the Earth-Two Superman destroyed it in INFINITE CRISIS, Batman carried a Kryptonite ring at all times as insurance in case a Kryptonian (most likely, Superman) ever went rogue.
Kryptonite is difficult to come by, even for someone of Batman's resources, but even if Batman could procure more Kryptonite for another ring...would he carry one these days? Before INFINITE CRISIS, Batman (Bruce Wayne) was in the depths of his paranoid phase, but he (and his relationship with Superman) has evolved since that time. Does Batman still feel the need to carry a Kryptonite ring around in his utility belt these days?
I'm pretty certain that the newer Batman (Dick Grayson) doesn't feel a need to carry one: it's not the way that Dick works, and his relationship with Clark has always been better than Bruce's.
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