${A\mathrm{V}}_3{\mathrm{Sb}}_5$ $(A=\mathrm{K}, \mathrm{Rb}, \mathrm{Cs})$ are kagome metals and superconductors, attracting much recent attention as the nexus of multiple quantum states. Here, through a systematic study of electric and thermal transport of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, we identify it as a metallic Fermi liquid with moderate electronic correlations and a strong electron-phonon (e-ph) collision cross section. We observe contributions to the inelastic electrical resistivity, each dominating within a distinct temperature window. The prefactor of $T^2$ is consistent with the Kadowaki-Woods scaling for a Fermi liquid with moderate correlation. By performing thermal conductivity measurements at zero and finite magnetic field, we separate the electronic and the lattice contributions to the thermal conductivity. The Wiedemann-Franz law is satisfied in the zero-temperature limit, while a downward deviation emerges at finite temperature due to the mismatch between the prefactors of the electrical and thermal quadratic resistivities, as reported in other metals. The Bloch-Grüneisen description of electron-phonon scattering successfully accounts for both electronic thermal and electrical transport, indicating a remarkably large e-ph collision cross section in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

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• Electrical conductivity
• Electron-phonon coupling
• Thermal conductivity
• Kagome metal
• Transport techniques