<p>This study investigated the turbulent natural convection heat transfer along a vertical plate experimentally for high Rayleigh number (<i>Ra</i>) of 1.3 × 10¹⁵ while the existing studies reached <i>Ra</i> ~ 10¹². To obtain high <i>Ra</i>, the electroplating mass transfer experiments using a copper electroplating system were utilized based on the heat and mass transfer analogy. This enabled us to reduce the facility height and relax experimental difficulties, in return the <i>Sc</i> corresponding to the <i>Pr</i> became 2,094. Experiments were conducted using a copper electroplating system. The measured Nusselt number (<i>Nu</i>) agrees well with existing correlations in the laminar regime, whereas deviations are observed in turbulent regime. To elucidate this behavior, the local heat transfer coefficient (<i>h</i>) was analyzed across different flow regimes by comparing with the existing works. In the laminar regime, the heat transfer behavior exhibits similar trends regardless of <i>Pr</i>. However, in the turbulent regimes, a dependence on <i>Pr</i> emerges. Especially, the heat transfer reaches a maximum when <i>Pr</i> is close to unity and decreases as <i>Pr</i> deviates toward either lower or higher values. This behavior is attributed to the variation in the thickness of the conductive sublayer with <i>Pr</i>. By compiling the present data with the existing data, a multiplier for the turbulent heat transfer correlation was developed to account for the influence of <i>Pr</i>. The proposed model shows improved predictive accuracy compared to existing correlations over a broader range of <i>Pr</i>. The developed correlation shows high accuracy across a wide range of <i>Pr</i>, compared to existing correlation, with a mean relative error of 3.2% and a maximum relative error of 13.4%.</p>