As you see a no matter how much you shop around, if you want a decent NiMH battery pack it will cost a decent sum of money. A saltwater flood would probably destroy the batteries so before taking them on a proper dive I tested the canister for leaks using lead shot bags as ballast. Newspaper is good for showing up any ingress of water. In the picture I have my canister assembled without batteries the light cord is in the gland but there is no lighthead.
I initially got some leakage at the cord gland but this was solved by tightening it up a little more. I submerged the canister in a large bin about 1M deep and left it over night just to be sure. There was no leakage.
My next test was without the battery pack in open water to 30M still without leakage. I have since been using the complete torch up to 40M with no problems.