not true according to this manufacturer.
"The Smart Battery SB80 is perfect for boats, trolling motors, cars and almost any application that would use a 12V 80AH lead acid, agm or gel battery. "
only 28lbs but for $1049 I ain't buying one anytime soon.
http://www.lithiumion-batteries.com/products/12v-80ah-lithium-ion-battery/[/quote]
It comes with "Fully automatic built in battery protection system" At 1049.00, I will stay with my AGM. My 5 AGMs bearly cost me that much.[/quote]
That looks very cool, and it's probably worth the price for some applications, but likely not most boats.
If their claims are correct, you might save some money by only needing 1/2 the battery for a house system, since deep cycle lead batteries aren't supposed to be drawn down more than 50%, and they claim it's OK to take theirs to 100%. Instead of 4 $250 AGM batteries you'd need 2 of these $1,000 LiFe units, so then they'd only need to last 3 times as long to be worth it!
[/quote]On the 50% draw down. Odessy AGM can go "up to 400 cycles at 80% depth of discharge"
There have been a couple of times were I ran the dead, recharged and came right back to life.
It was just a simple statement about lithium ion batteries being used in an off-road mobile 12V application, with good results. But hay, for those that like me that dont know anything about boats or race cars, please explain how they are different 
I mean, hour into the race, the alternator belt flies of. Now, that battery has to support brake rotor cooling fans, electronic ignition, ECM and injectors, electric fuel pump, etc, etc. Yep, nothing like house loads on a boat. 