To draw maximum current from a combination of cells, the cells should be grouped in

$\mathrm{Current} \mathrm{J}=\frac{\mathrm{Net} \mathrm{e}.\mathrm{m}.\mathrm{f}}{\mathrm{Net} \mathrm{Resistance} }=\frac{{\mathrm{E}}_{\mathrm{net}}}{\mathrm{R}+\mathrm{r}}$r is the Internal Resistance

R is the external Resistance

When net external resistance is far greater than net internal resistance, then to get maximum current, cells must be connected in series

A parallel combination of cells is useful when the internal resistance is far greater than external resistance and large current is required.