12v batteries sold at shop and online with 12v labelled are actually higher than 12v when charged (10 cells * 1.2=12v since each cell is 1.2v nominal, but often 1.4-1.5v when charged). Commercially labelled 12v nimh packs are allowed right in this...
Per rule 3d, the ES is to calculate voltages based on the manufacturer’s original labels on the batteries.