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The ultra-diffuse galaxy in the NGC 5846 group (NGC 5846_UDG1) was shown tohave a large number of globular cluster (GC) candidates from deep imaging aspart of the VEGAS survey. Recently, Muller et al. published a velocitydispersion, based on a dozen of its GCs. Within their quoted uncertainties, theresulting dynamical mass allowed for either a dark matter free or a dark matterdominated galaxy. Here we present spectra from KCWI which reconfirms membershipof the NGC 5846 group and reveals a stellar velocity dispersion for UDG1 of$\sigma_{GC}$ = 17 $\pm$ 2 km/s. Our dynamical mass, with a reduceduncertainty, indicates a very high contribution of dark matter within theeffective radius. We also derive an enclosed mass from the locations andmotions of the GCs using the Tracer Mass Estimator, finding a similar massinferred from our stellar velocity dispersion. We find no evidence that thegalaxy is rotating and is thus likely pressure-supported. The number ofconfirmed GCs, and the total number inferred for the system ($\sim$45), suggesta total halo mass of $\sim2 \times 10^{11}$ M$_{\odot}$. A cored mass profileis favoured when compared to our dynamical mass. Given its stellar mass of1.1$\times$10$^{8}$ M$_{\odot}$, NGC 5846_UDG1 appears to be an ultra-diffusegalaxy with a dwarf-like stellar mass and an overly massive halo.

Stellar Velocity Dispersion and Dynamical Mass of the Ultra-Diffuse Galaxy NGC 5846_UDG1 from the Keck Cosmic Web Imager