Battery capacity

What it means

Battery capacity is the amount of energy a boat carries, measured in kilowatt-hours (kWh). It is the single figure that decides how long you can stay out, and on an electric boat it does the job that tank size does on a combustion one.

Nominal and usable are not the same

A pack described as 50 kWh rarely delivers 50. Manufacturers reserve a margin at the top and bottom of the charge to protect cell life, so the usable figure is typically lower — sometimes by a tenth, sometimes by a fifth. Some builders publish the usable number, some the nominal, and most do not say which. Where a builder has not told us, we leave the field empty rather than assume.

Why it matters

Capacity alone tells you nothing about distance; it has to be read against the power the boat draws at the speed you intend to travel. A large pack on a heavy planing hull can give less useful range than a modest one on an efficient displacement hull.