In the above I should add the ultimate durability and "abusability" of the NiFE is unparamounted. The charge voltage can vary from 1.46 to 1.55 volts per cell. Unlike other battery designs, the exact charge voltage is unimportant. A higher voltage will result in quicker charges but more water loss that will necessitate more frequent topping up with distilled water. So in theory, anyways 4 cells in series should work quite nicely.
I suspect this setup would provide free light for 40-50 years without part replacement.