Most model variants ask you to weigh a list of differences. This one asks you to weigh exactly one, and Scout is unusually direct about it: the company's own model page calls the 400 LXF Li-Ion "a new model and alternative version to the current 400 LXF, complete with a lithium ion battery management system (no generator necessary)." Everything else about the two boats is the same, and Scout's published numbers prove it rather than imply it.
The same boat on paper
The 400 LXF and the 400 LXF Li-Ion publish an identical length of 39 feet 7 inches, an identical 12-foot-1 beam, an identical approximate 27-inch draft and an identical 22 degrees of transom deadrise. Both list 14,940 pounds dry without engines and 17,460 pounds rigged with twin Mercury 600s. Both list 395 gallons of fuel standard and 509 with the optional saddle tanks, 51 gallons of fresh water, a 16-gallon waste tank, 66 gallons of baitwell and 92.5-gallon aft fish boxes port and starboard. Both publish 6 feet 4 inches of cabin standing room, 6 feet 3 in the head and a 6-foot-5 berth. Both are rated to 1,700 horsepower, both are S-Class, both are NMMA and Yacht Certified.
The one line that changes: the 400 LXF carries an 18-gallon diesel tank to feed its generator, and the Li-Ion carries none, because there is no generator aboard. That is the whole difference.
What comes out, what goes in
On the 400 LXF, the standard electrical package is an 8 kW diesel generator on that 18-gallon tank, three AGM house batteries, two 50-amp battery chargers and a Seakeeper 3 DC. The option sheet offers a 5 kW generator as a downgrade and a 12 kW as an upgrade.
On the Li-Ion, the standard package is a 48V lithium-ion system, C-Zone digital switching, a Xantrex Truecharge 3 battery charger and a 50-amp shore power plug. A generator is not offered at all - not as standard, not as an option, not as a delete credit. Scout's page states the batteries are charged by the Mercury engines as well as from shore power, and hardtop solar panels sit on the option list as a third source.
The standard gyro also grows. Scout's Li-Ion page describes a standard Seakeeper 5 DC with an optional upgrade to a Seakeeper 6; the 400 LXF page describes a standard Seakeeper 3 DC. Note that Scout's own Li-Ion model flyer lists the standard unit as a Seakeeper 4.5 rather than a 5, so confirm the size on your build sheet - but on both documents it is a DC unit, which is the relevant part on a boat with no genset.
What Scout actually documents about the batteries
This is where the Li-Ion material is better than most. Scout links a battery safety statement from the model page, and it names the hardware: Fathom is powered by Mastervolt batteries built to the ABYC E-13 marine standard, using lithium iron phosphate chemistry rather than the chemistry common in automotive packs. The Mastervolt MLI Ultra batteries carry a built-in battery management system that monitors voltage, current, temperature and state of charge, protects the cells against overcharging and over-discharging, and includes a safety disconnect that stops charging and disconnects loads if a safety event is triggered. The cells are certified to UL 1973, a third-party standard for batteries used in energy storage systems.
That is more provenance than a buyer usually gets, and it is worth reading before anyone tells you lithium on a boat is an unknown quantity.
Three figures belong on your build sheet in writing: the bank's capacity in kilowatt-hours, its amp-hour rating, and the run-time for the standard 12,000 BTU air conditioner at anchor. If silence on the hook with the cabin cold is the reason you are buying this boat, settle all three before you sign.
The one bulletin that counts
Scout has tested this boat once with the lithium system aboard. The bulletin is titled "400 LXF Li-Ion w/ Seakeeper & Fathom" and covers triple V10 Verado 400s on Rev X stainless props in 25p, 23p and 25p, run on 24 March 2025 with four aboard at an approximate full-boat weight of 18,640 pounds - which Scout notes includes a quarter tank of fuel, the Seakeeper, the hardtop and the lithium battery management system.
Top speed is 62.7 mph at 6,400 rpm. Zero to 20 mph takes 6.34 seconds and zero to 30 takes 9.89. The economy figure is the interesting one: 0.87 mpg at 4,000 rpm and 36.6 mph, and the same 0.87 mpg at Scout's marked best cruise of 4,500 rpm and 43.4 mph. That is a band roughly seven miles per hour wide where the boat does not care where you sit, which is worth more on a real day than a single peak on a chart. Scout's estimated range on the sheet is 343 miles, or 442 with the optional saddle tanks, footnoted as an estimate.
Which range figure is this boat's
The Li-Ion model page's specification table lists estimated range as 355 miles, and 458 with saddle tanks, credited to quad Mercury 400s and a Seakeeper. Those numbers come from the 400 LXF's bulletins, computed on 430 gallons, and neither test had the lithium system aboard. The Li-Ion's own bulletin says 343 and 442, and those are the figures used throughout this guide. It is a 12-mile difference and nobody's purchase turns on it, but if you see 355 quoted for a Li-Ion, now you know where it came from.
The same page also links the quad Mercury 400 V10 and twin Mercury 600 V12 bulletins. Both are titled 400 LXF, neither mentions Fathom, and both print 430 gallons and a 1,600-horsepower ceiling against the 395 gallons and 1,700 horsepower on the current page and flyer. The Li-Ion's own bulletin also prints 1,600. Use the current spec block, and confirm the tank on the build sheet for your model year.
The cost of the choice
Run the comparison on power rather than on badges. Triple Mercury 400 V10s make 1,200 horsepower, and the twin Mercury 600s Scout also lists make the same 1,200. Top speed is effectively a tie - 62.7 mph on the triples against 62.6 on the twins - but the twins reach 30 mph in 7.88 seconds against 9.89, and the quad 400 package on the 400 LXF does it in 7.31 and tops out at 71.5. The test conditions differ, and that matters: the twin-600 sheet was run with six aboard on half a tank, the quad sheet with one person aboard, and the Li-Ion sheet with four aboard on a quarter tank. Treat the acceleration gaps as indicative rather than clinical.
The honest summary is that the only tested Li-Ion configuration is the slowest-accelerating of the three sheets on this hull, and also the only one with a documented lithium house system underneath it. That is the trade. It is not a weight trade - Scout publishes 14,940 pounds dry for both boats.
Which of the two 400s
Take the 400 LXF if you want the quad-400 acceleration, if you want three tested engine packages to argue over, or if you want an air-conditioning architecture whose behaviour at anchor is entirely predictable because a diesel engine is making the power.
Take the Li-Ion if the generator is the part of the boat you have quietly dreaded owning - the day tank, the service interval, the noise at 2 a.m. - and if you would rather have documented lithium hardware than an unknown. You give up nothing on deck, nothing in the cabin and nothing in the tank. You give up the diesel, one row on the spec table, and about two and a half seconds to 30 mph.
Everything else is the same 39-footer, and the decision is genuinely just the one.