It is interesting that you focus mainly on LiFe batteries. In my opinion they are the worst value for money out there. Yes they are light but that is about the only good point they have.
In a yacht a good set of AA or AAA NiMh batteries formed into a 4 cell (4.8V) or 5 cell (6.0V) will generally set you back far less and as long as you look after them they will last a good 5 years or more.
I recently had to replace 1 cell in a 5 cell AA pack (that I use primarily in my larger yachts) that was made with cheap HobbyKing NiMh cells way back in September 2012.
Most transmitters (but not all) will take 4 (or sometimes 8) individual AA batteries and 4 x AA NiMh fit this bill also. Yes they only produce 4.8V and not 6.0V but they will still keep your transmitter running for many days of sailing.