Rechargeable Batteries For Snorkel Lights
I highly recommend rechargeable batteries for snorkel lights. So try to buy one that will use AA or AAA batteries. In Galen and Nicole's snorkel light article they suggest that infrequent use will cause the batteries to lose their charge while in storage. This is true for older technology rechargeables, and this is partially true of alkaline batteries. But there are better quality batteries available.
The keys to buying good quality rechargeable batteries is that you want the newer generation "low self-discharge" or LSD batteries. They only lose 10-20% of their charge over the course of a year (or longer). My experience with LSD AAs for my camera is night-and-day compared to Energizer or Duracell rechargeable AAs. My camera can now sit for months, and still be ready-to-use. Before, with the Energizers, the batteries would be totally dead after a month of storage.
If shopping at Amazon, look for batteries reviewed by "NLee the Engineer" who, incredibly, buys just about every battery available and puts them through a series of tests, including long-term storage. Good LSD AAs will cost just $2 each. But, you also need a good quality charger, so add another $10. Not a terrible expense since I'm sure that 95%, or more, of snorkelers out there care about the environment and their environmental impact!