EPR spectra of aqueous solutions of the singly charged surfactant nitroxide 4-[N,N-dimethyl-N-(n-dodecyl)ainmonium]-2,2,6,6-tetramethylpiperidinyl-N -oxy bromide-d(16) (DCAT12) are studied as functions of the molar concentration, c = 0.1-8 mM, and the temperature from 273 to 353 K. This concentration range is below the critical micelle concentration, cmc, at which DCAT12 forms micelles. Spin-spin broadening of the EPR lines averaged over the three lines is separated into contributions due to spin exchange, < B-e >, and dipolar, < B-dip >, interactions yielding values of the fractional broadening by spin exchange, Omega(T), that vary from near unity at 353 K to approximately 50% at 273 K. This compares with a variation from unity to approximately 77% for a neutral spin probe perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (PDT) over the same range. Unlike PDT and the Stokes-Einstein prediction, the broadening constant by spin exchange, d < B-e >/dc, is not linear with T/eta, where eta is the shear viscosity, instead following a quadratic dependence. Nevertheless, d < B-e >/dc is remarkably close to a hydrodynamic prediction using the Stokes-Einstein equation modified to take the spin probe charge into account. Compared with PDT, values of d < B-e >/dc are decreased and d < B-dip >/dc increased at all temperatures, while the values of the re-encounter rate, tau(-1)(RE), deduced from line shifts, are reduced. Interestingly, values of d < B-dip >/dc, Omega(T), and tau(-1)(RE) are comparable for PDT and DCAT12 when compared at the same rotational diffusion rates.