I do have a charger on my 9.9 outboard - need for the more expensive LED lights?
Unless your sailing at night, you don't need the nav lights being LED, if your running the engine. The alternator on the engine is more than ample for any light you may be using, LED or not. Even if your only using the lights for a few hours, with a good battery, there'll be no problem. I've rarely sailed at night, much preferring a sheltered cove or bay to relax in. Chargers on the old smaller outboards are usually 6 amp, the newer ones are 10 amp. I've replaced the cabin lights with LED's cause I DO use these with the anchor down, sometimes for 4 or 5 hours at a time (also keep the GPS powered all night for the anchor alarm it has). In the past I've only had 1 battery but it was an Optimus blue top deep cycle D31M & had absolutely no issues with power, but I always carried a second portable one on board to start the engine if needed. (never did). This year I put a second bank in, for 3 reasons; 1) obvious extra power, 2) more weight down lower in the boat, 3) balancing the C of G so I can load the boat on to the trailer easier.