I have spent some time researching the Lithium VS conventional battery debate, here are some of the facts I found and places one can do there own research to educate themselves, if they care to be educated:
1. Lithium Ion seems to be the safest of the lithium group of battery types, but it's not impervious to failure. If it has a failure and experiences a "thermal runaway" you can guarantee there will be damage to whatever item the battery is mounted in. Also, the fire can be very difficult to put out. Conventional batteries have no issue with this. Electrical fires on boats due to voltage supply with conventional batteries are due to dead shorts and the wires/insulation heating and starting a fire.
2. No one can argue LiIon does not have better cycling characteristics than conventional batteries. They typically hold useful charge longer due to retaining the amount of voltage typically required by the item draining them. They retain their percentage of recharge, and can go through more drain/charge cycles than conventional batteries. When they are exhausted and need recharging, the end is sudden, complete, and without warning.
3. They are very expensive. (maybe disproportionately) This due to manufacturing costs, import costs, multiple layers of markup, and other behind the scene items. For example, a Lithium Pro single 36V 40 AH battery is advertised at $2,199.00. Locally I can buy three 12 V Deka (East Penn) AGM group 31 batteries at $230.50 each, (add $15 if no core) for a total of $691.50. This is 31.5% the cost, or in other words, it would cost over 3 times as much to use LiIon in this case. Thus, for the same investment, maybe less due to core refunds, I can replace the batteries 2 more times. I currently have a large boat with AGM's that I have been running going on their 6th season.
4. LiIon battery companies are smaller companies who are not manufacturing 100% of their product. They are typically "assembling" the batteries with the components purchased elsewhere.(asummably from outside the US) From what I have ascertained, the largest risk for catastrophic failure in LiIon batteries is in the manufacture of the layered "wafer" cells. These need to be manufactured in a "clean room" environment so no metallic particles get introduced between the layers of lithium and insulator. There is nothing "wrong" with purchasing from a smaller company, this is the USA and that's what we are built on. For conventional batteries, I am sure someone could buy them from Wally World and get (cheaper?) units made in an economy outside the US. But if I look at East Penn, a company who's products I have purchased before and used as example in point #3, they are a US family owned company employing American citizens at all levels of manufacture. For warranty standpoint, as long as the smaller company has longevity or "horsepower" behind it, it should be good. I would assume reading the fine print would be in order, and the odds of getting issues resolved long distance VS locally would come into play too.
5. Weight and overall loading is one place LiIon kills the competition. Battery for battery one will save approximately 30# of total loading. If you look at the example above, where 3 conventional batteries are compared to one LiIon, there are substantial savings. The LiIon is advertised at 30.3# and the AGM batteries are 67.5# each. This yields a difference of 172.2# less load. Or the LiIon is only 15% the weight of the three AGM batteries.
6. Recycling, for conventional any retailer will take your core and hand you some cash, typically $15.00. For LiIon I have found a lot of conflicting info ranging from you can drop them at local recycling centers (no refund) to one may have to pay to dispose of larger batteries such as the type we are discussing here.
For anyone who cares to educate themselves further on batteries, I strongly suggest you go to the battery university site
http://batteryuniversity.com/learn/
There is a great deal of info there.
For info on individual companies, Google is your friend. Just put a few minutes of effort in and you can trace down most of what you care to find out.
For myself I will be rigging with conventional AGM batteries. I would love the weight savings but for the cost VS the unknown VS potential warranty issues, LiIon doesn't feel promising enough. I also assume there are new battery "breakthroughs" coming and the AGM's will get me through the next 5 years, in which time I expect something different to be on the market. In the mean time the $ for LiIons will be redirected for addition square inches of electronic underwater displays.