I'm working on a few LiIon new build projects now. I've approached this technology cautiously, I did not embrace it like some of my author colleges, especially not for propulsion, and still don't. I can recall, 12 or 15 years ago when hybrid was all the rage, asking boat builders who were going down this path, why are you doing this, it isn't more efficient? The standard response was almost always, "Cruise ships and tug boats use it". That was the logic. All of those builders, there were only a few thankfully, found out the hard way that a yacht is not a cruise ship or tug boat. In very limited applications, hybrid propulsion afloat makes sense, but it's a narrow slice and very few are recreational. In the vast majority of cases it's a net loss when compared to a diesel, with vastly increased expense and complexity added on top of it.
So, Wes, I agree, for propulsion LiIon on boats makes little sense at this point unless you have a very large solar array (and some do, Greenline, with limitations of course, can run on solar alone), as there is no regenerative aspect.
At this stage in its life I believe LiIon has now progressed from bleeding to leading edge technology, at least within the recreational marine field.
Having recently spent three weeks aboard a 75 foot cruising vessel whose house 2000 Ah bank is LiIon, I can say it does offer a number of advantages for this application, with some caveats. After 17 hours at rest, the bank aboard this vessel was at 50%, and that included use of the induction cook top, everything in fact except HVAC. Unlike lead acid batteries, 50% is not the recharge threshold, Li Ion batteries can be depleted to 20%. Recharge time is also blinding when compared to AGM. Lifespan is multiples of lead acid banks, they weigh significantly less and because of their DoD, a smaller bank can essentially do the same work when compared to lead acid.
As I said, there are caveats, they remain very expensive, few professionals understand them or the charging systems, making retrofits, troubleshooting and repair problematic, they rely on a lot of monitoring, automatic controls and technology to remain safe, and safety is a concern as an overheated LiIon battery has a significant chance of leading to a fire. It's also worth noting, there are a number of LiIon chemestries, those used in most marine applications are, unlike cars and the B787, lithium iron phosphate (LiFePO 4).
ABYC is in the midst of writing a standard for LiIon battery installations. I know of at least two builders who have said they will go Li Ion once a standard is available.
IMO, the only way to do this with any degree of safety is by using a complete package from one manufacturer, batteries, chargers, inverters, monitoring etc. And, the installation, once complete should be inspected and approved by the manufacturer (not necessarily a dealer unless he or she is a confirmed expert in these systems, and is capable of scrutinizing the installation for flaws, been there done that).
Bottom line, a boat is not a car, diesel engines remain, with few exceptions, the best, most reliable, safest and most efficient means of propulsion for now. For house batteries, however, the industry continues to edge closer and closer to Li Ion adoption. Right now, the biggest limiting factor is price, if/when that comes down I'm pretty certain we'll see widespread adoption. Unless of course a better battery technology comes along;-)
