We present the ionised gas properties and metallicity gradients of the central area of a sample of 43 galaxies using observations obtained by the MEGADES survey. The technical capabilities of MEGARA (Multi-Espectr & oacute;grafo en GTC de Alta Resoluci & oacute;n para Astronom & iacute;a) provide us with relatively high spectral (R similar to 6000) and spatial (0.62 '') resolution observations that we used to study the properties of the ionised gas via various methods, including using the classic diagnostic BPT diagrams of its [N II] and [S II] variants. We explore how the diagrams vary as a function of both the radius and velocity dispersion of the H alpha line. We also propose a new diagnostic diagram for assessing the relative contributions of active galactic nuclei (AGN), shocks, and H II regions in each spatial region as the ratio between the velocity dispersion of the [N II]lambda 6584 and H alpha lines. A considerable number of regions, regardless of their galactocentric distance, have emission line spectra associated with shocks. This inference follows both from their line ratios, typically characterised by high [N II]lambda 6584/H alpha and intermediate [O III]lambda 5007/H beta, and from their position in our diagnostic diagram, where they lie between the areas associated with HII regions and with AGN. The better selection of HII-region-like emission allowed for a robust oxygen abundance determination using the N2 indicator, which we used to measure precise abundance gradients. Most galaxies show negligible metallicity gradients, especially the low-abundance (< 8.37 dex) fast rotators. The mean value of the slope of the metallicity gradients for this subset is 0.005 dex R-e(-1), with a dispersion of 0.422 dex R-e(-1). Above 8.37 dex the fast rotators consistently show slightly negative metallicity gradients, with a weak correlation between the slope and the y-intercept. The mean slope of these galaxies is -0.681 dex R-e(-1), with a dispersion of 0.933 dex R-e(-1). The overall mean value of the gradients for all galaxies in the MEGADES sample is -0.025 dex R-e(-1), with a dispersion of 0.766 dex R-e(-1). We discuss the possible implications of these results regarding the impact of galactic winds on the abundance gradients of galaxies.