46 CFR §161.013-9

1. (a)Each independent power source must be capable of powering the light so that it meets the requirements of § 161.013-3(a)(1) and emits a recognizable flash characteristic of the International Morse Code for S-O-S at a rate of between 3 and 5 times per minute after six hours of continuous display of the signal.
2. (b)If the independent power source is rechargeable, it must have a waterproof recharger designed for marine use.
3. (c)If the independent power source requires external water to form an electrolyte, it must operate in sea water and fresh water.