Or bring two or more "primary" handheld lights as needed to reach the total burn time needed. Aggregate size, weight, cost, would be advantageous compared to canisters.
Each of the lights will need an attachment point, battery charge label, a reliable storage system to distinguish between spent and fresh ones, and a separate charger. How many are we talking about? Caves aside, a full day of liveaboard diving will easily give you 4-5 hours in the water.
As a side note, on project dives we use a 10,000 lumen video light fed by a 29V, 17Ah canister battery which gives ~3,5-4 hrs of burn time. That thing is about the size of a pony bottle, and in fact some divers choose to attach it as such. I don't think such battery is easily substituted with anything substantially smaller without a massive loss in burn time and output.
Finally, many divers feed their heating systems from canister batteries, often enough from the same batteries as their main lights.