Lithium metal batteries (LMBs) have been revisited and gained great attention due to significantly mitigated formation of Li dendrite in the past decade. Recently, anode-free lithium metal batteries (AFLMBs) are proposed and have been studied intensively to potentially outperform LMBs due to higher energy density and reduced safety hazards since the absence of Li metal during the fabrication process of the cell. In general, researchers compare capacity retention, reversible capacity, or rate capability of the cells to study the electrochemical performance of batteries. However, evaluating the behavior of batteries from limited aspects would easily overlook other information hidden deep inside the meretricious results or even lead to misguided data interpretation. In this work, an integrated protocol combining different types of cell configuration is proposed and validated for the first time to unravel the concealed messages in LMBs and AFLMBs. Irreversible coulombic efficiency (irr-CE) from various contributions including reductive electrolyte decomposition, dead Li formation, 1st intrinsic irreversible capacity of a cathode, and the subsequent irreversible reactions at cathode containing oxidative electrolyte decomposition and cathode degradation upon cycling are successfully determined separately by the integrated protocol for the first time. The decrypted information obtained from the proposed protocol provides an insightful understanding of behaviors of LMBs and AFLMBs, which promotes their development for practical applications.