Options 6 and 7...
Main primary light is an UWLD and gets rinsed when it's been in salt water, then put on the charging base. No need to open the battery case except for periodic inspections, one of the great things about that light. Cold water backup primary light is a DR head with a connector to my DUI Blue Heat battery. It just gets disconnected and then rinsed if in salt as well. Backup lights are DRIS 1K lumen handheld lights powered by alkaline C cells. They get tested at the start of every dive, and batteries changed a couple of times a year. They only get rinsed as well after diving in salt.
Then there's the other (warmer water) backup primary light, a LM. The canister gets opened post-dive, the battery disconnected, and the canister resealed. Later, it gets rinsed if it's been in salt water, taken apart immediately afterward, and the battery put on the charger. No need to wait for it to dry since essentially no water gets to the battery and the battery case is completely dry by the time the battery is fully charged. It gets put together with the battery disconnected, and taken apart to connect the battery just before use.