We report on a study of the superconducting properties for a series of polycrystalline BaPt_4–xAuxGe₁₂ filled skutterudite compounds for x = 0, 0.5, 0.75, and 1. Muon spin rotation (μSR) spectroscopy as well as magnetization, specific-heat, and electrical resistivity measurements were performed. The magnetic penetration depth λ, the coherence length ξ, and the Ginzburg-Landau parameter κ are evaluated. The temperature dependence of the superfluid density is well described by an s-wave superconducting gap and this classical scenario is supported by the field-independent λ. The gap-to-T_c ratio Δ₀/k_BT_c increases with the Au content from 1.70 for x = 0 to 2.1(1) for x = 1. By combining μSR, magnetization, and specific-heat data, we find that BaPt_4–xAuxGe₁₂ compounds are in between the dirty and clean limits with mean free paths of the carriers l ~ ξ. Interestingly, resistivity data for BaPt_4–xGe₁₂ indicate a much higher upper critical field, which is probably due to defects or impurities close to the surface of the crystallites.