<p>In the Hall–Heroult process for primary aluminum production, the generation of anodic bubbles is an inherent phenomenon during electrolysis. This study investigated bubble dynamics and its impact on voltage drop in aluminum electrolysis cells. A bottom-observation transparent electrolysis cell was employed to enable direct visualization of gas evolution processes. Bubble nucleation, growth, coalescence, and detachment processes were recorded used high-speed cameras, and key parameters (size, coverage) were quantified through image analysis. The results showed that bubble growth preferentially occurred at localized surface regions over a short-term period. Coalescence between adjacent bubbles was identified as a dominant mechanism for bubble growth, which resulted in bubble diameters ranging from micrometric to millimetric scales. The bubble coverage exhibits a nonlinear decline with increasing current density, reaching a minimum value of 50% ± 2% at 0.9 A cm⁻². This minimum coverage indicated a balance between bubble detachment and bubble generation. Synchronized voltage monitoring demonstrated a strong correlation between voltage fluctuations and bubble dynamics. The bubble-induced resistance was governed by both bubble coverage and bubble size, highlighting limitations in existing models that neglect bubble size effects.</p> Graphical Abstract <p></p>