The science
Zinc is won from acid sulfate solution: Zn2+ + 2e- -> Zn at the aluminium cathode and 2H2O -> O2 + 4H+ + 4e- at the lead-silver anode. Faraday's law gives the deposited mass
m = eta I t M / (z F), z = 2, M = 65.38 g/mol, F = 96485 C/mol
The cell voltage is modelled as the sum of the decomposition voltage (1.99 V for Zn/O2), the electrode overpotentials (an adjustable lump) and the ohmic drop j d / kappa across the electrolyte gap. Specific energy is V z F / (eta M), about 3 kWh per kg for typical settings.
Honest simplifications: current efficiency is an input, not predicted from impurities or acid level; the current is assumed uniform over the plate (no edge effects or dendrites); bubble void fraction in the gap and temperature effects are ignored. Each cathode is taken as 1.6 m2 per side. Checks compare time-integrated mass, thickness and energy with the closed forms.