Solid-State Batteries for Boaters

Solid-state batteries from Solid State Marine feature a thin, solid lithium electrolyte coating that saves weight and boosts capacity. Courtesy Solid State Marine

As recently as this past winter, solid-state batteries were touted as future tech poised to move electric propulsion rapidly forward. Jumping ahead a year, Honda ­announced limited production of these new-generation batteries sometime early in 2025. But, Boating had already tested solid-state batteries in the Electric Legacy, a classic runabout replica collaboration between Elco and Lancer Craft. So, what did we discover about this technology and how it might benefit you?

What Is a Solid-State Battery?

In most batteries, be they lead-acid or lithium, liquid electrolyte facilitates energy transfer between cathode, anode, and electrical equipment. ­Solid-state ­batteries still employ lithium, but the electrolyte is an ultra-thin solid coating. “The US government has been using solid state for 20 years,” says Tom Calef, founder and CEO of Solid State Marine. “The issue has been manufacturing. If that nano-thickness coating isn’t the same every time, you’ll have one cell that stores 100 watt-hours, and the next has only 10.” With those challenges overcome, Calef says his company now offers solid-state marine batteries at competitive prices in voltages and sizes common for marine applications.

The construction of solid-state batteries offers several advantages. AllahFoto / Adobe Stock What’s Better About Solid State?

Solid electrolyte coatings make solid-state batteries about half the weight of today’s lithium-iron-phosphate (LiFePO4) batteries for the same stored power. There is a bigger advantage though. “It takes a lot less energy to push through a solid material than it does a liquid,” Calef says. That reduced electrical resistance pushes power ­considerably faster from solid-state batteries into electric motors, while generating less heat in the exchange. 

That’s a game-changer: It gives electric-boat motors—and other high-draw marine electrical accessories—all the amps they need. This is especially critical when an electric-powered boat is climbing on plane. An analogy might be running your gas-powered boat with undersize lines or clogged fuel filters. Switching to solid-state batteries is like refitting the entire fuel system and tripling the flow. By starting with much lower resistance, solid-state batteries also continue to provide required amps through their entire capacity even as battery voltage drops and resistance climbs, Calef says, increasing usable watt-hours. Another fuel analogy? It’s like having a pickup tube 20 percent too short on your fuel tank but then getting a new one that goes all the way to the bottom.

Electric Propulsion Benefits

I assumed that an electric Lancer Craft might barely top 25 mph. Replacing gas-powered batteries with wet lithium ­batteries adds some 800 pounds to the original designed weight. That’s hard for a 20-foot runabout to overcome. Instead, the eight solid-state batteries—at 103 pounds each, plus Elco’s 205-pound motor and equipment—weigh 10 percent less than the GM small block, transmission, and full fuel tank. Less weight and more watts result in impressive hole shots and 35 mph top speed, albeit with less range than gas.

A single solid-state 210-amp-hour 12-volt battery can power a Seakeeper 2 gyrostablizer for a much longer time than three AGM batteries. Courtesy Solid State Marine What About Other Applications?

In any application, solid-state batteries roughly double conventional LiFePO4 battery run time for the same weight. Both options—solid-state and LiFePO4—offer bigger gains when consolidating battery banks. In one example aboard a 32-foot SeaVee charter boat, Capt. Tristan Raynes replaced three 12-volt AGM 31 series batteries powering his Seakeeper 2. Just one fully charged 27 series battery from Solid State Marine rated at 210 amp-hours lasts an entire charter; in the past, with the three AGM batteries, he needed to run the SeaVee’s twin 300 hp Mercury Verado outboards continuously to power the Seakeeper 2. The boat’s aging LiFePO4 trolling-motor batteries were also ripe for upgrade. Raynes’ Minn Kota 36-volt trolling motor required three conventional LiFePO4 batteries, which didn’t always last all day. Now, just one 31-series solid-state battery increases run time by 20 percent. Today’s newest LiFePO4 batteries offer similar consolidation. “I replaced six batteries with just two and took 400 pounds off the boat and added capacity,” Raynes says.

A solid-state battery possesses a similar lifespan to a conventional lithium battery, retaining 95 percent capacity after 1,500 cycles. Capt. Vincent Daniello Longevity and Charging

Calef expects similar lifespans for both solid-state and conventional lithium batteries, retaining 95 percent capacity after 1,500 cycles and 75 percent after 2,500 total cycles. That’s a full discharge every day for seven years. Most ­off-the-shelf lithium-battery AC chargers are compatible with Solid State Marine batteries; Calef mentions NOCO and Victron as examples. 

Calef also sees safety gains. Though today’s conventional LiFePO4 marine batteries have enjoyed a remarkable safety record to date, it is conceivable that a pierced LiFePO4 battery could ooze electrolyte that could create shorts and overheat the cells, potentially causing a thermal chain reaction. The solid electrolyte in a solid-state battery won’t leak, thus preventing a short if pierced. Of course, large power sources are problematic around seawater, and salt water contacting lithium directly in any battery type creates volatile hydrogen gas.

Calef sees boat systems moving steadily toward lithium. “In so many applications, lithium technologies are dramatically better in storing electrical energy than lead,” he says. “With solid-state batteries, we’re bringing more of the benefit of lithium to the ­boating market.”

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