About two years ago I switched to 6.6 volt Lithium Iron (LiFe) batteries. LiFe batteries are not "LiPos".
LiFe batteries start out at an initial voltage of 6.6 - 6.7 volts. This is actually the same starting voltage of a (6 volt) NiMH battery. LiFe batteries are much superior, however, in that they maintain essentially CONSTANT VOLTAGE as they discharge. So after an hour or two they still read 6.6 volts. After 4 hours they still read 6.6 volts. With an NiMH battery the voltage will drop as it discharges. So after a couple of hours, the voltage is down to 5 volts and everything in the boat gets slower or quits, just when you don't want it to!
Conversely with a LiFe battery, the winch and servos in your EC-12 will run with the same power after 2 hours, 4 hours or 6 hours.
I have used LifeSource LiFe batteries from Tower hobbies. They sell an 1800 mAh battery that will easily go 6+ hours in an EC-12. A LiFe charger is REQUIRED! Tower sells a simple LiFe dedicated charger for $35. Simple, small and foolproof.
There are numerous other benefits to LiFE batteries. They charge in 15 minutes. They hold full charge for 7-14 days.
And no need to worry about voltage regulators or other stuff. Just plug in and go.
I wrote an article on LiFe batteries a while back. The article contains voltage data charts, chemistry explanations, etc. More than you probably want to know. If interested, I can email a copy. Contact me directly at RJHEDDERICK@comcast.net