At the moment those batteries are usually either alkaline or lead-acid. Lithium-ion batteries, fashionable elsewhere, have not conquered the UUV world. Their tendency to catch fire counts against them. And they are sensitive to pressure, which is undesirable in devices that operate underwater.
But a firm in Somerville, Mass., called Open Water Power (OWP), is offering an alternative: batteries based on aluminium. With these, its engineers hope to extend the ranges of underwater drones tenfold.