The increased use of lithium-ion chemistry batteries on land has had a parallel trend in the marine world. Lithium-ion batteries, which were considered highly exotic five years ago, are becoming ever more commonplace on voyaging boats. What are the reasons for this trend and how widespread is it?
The longtime king of marine batteries, of course, is the lead acid cell. Using a liquid electrolyte and lead plates, each of which is a matrix generally filled with soft lead, the wet cell marine battery ruled supreme for its stability and its storage capacity. Different types of wet cell units were developed for various tasks. Starter batteries, for example, have thin plates with lots of surface area exposed to the electrolyte that provide a quick jolt of power. Deep cycle lead acid batteries tend to have thicker plates and are designed to handle the physical wear and tear on a battery when it is deeply discharged. The heavy duty elements of this type of lead acid battery are built not only to handle higher levels of discharge than starter type batteries but also to ride out repeated cycles of discharge and recharge. Deep cycle might be a bit of a misnomer, though, because these batteries in normal use are recommended to be discharged to roughly 50 per cent of capacity. Repeatedly discharging a lead acid battery beyond that level can physically damage the battery.
Lead acid battery tech has evolved from standard wet cells to the use of a gelled electrolyte called a gell cell battery. Another important battery design is the absorbed glass mat (AGM) unit. In this type of battery the electrolyte is absorbed into a fiberglass mesh. Like gell cell batteries, AGMs don’t require maintenance in the form of checking electrolyte levels and topping them up. These types of batteries also can be installed in any orientation, unlike wet cells which must remain upright.
Lithium-ion chemistry batteries, which use a lithium salt and an organic electrolyte, have lately become an important trend. Several aspects of lithium-ion batteries that make them attractive are their ability to handle deep discharge, their flat discharge curves, rapid recharging times and lower weight when compared to lead-based batteries. In addition to the ability to discharge them below 50%, a lithium-ion cell will generally provide its nominal voltage until nearly completely discharged. And they can be recharged faster than a comparable lead acid battery. Plus, unlike a flooded lead acid battery, lithium batteries are similar to gell cells and AGMs in that they are sealed and need no additional electrolyte.
There are a variety of lithium-ion battery chemistries, with lithium-ion polymer mixtures most frequently used for consumer electronics. For marine applications, lithium iron phosphate (LiFePO4 also known as LFP) has become the chemistry of choice, although there are also many lithium nickel manganese cobalt oxide (commonly abbreviated NMC) batteries in use. The popular Torqeedo electric outboard uses NMC batteries, for example.
The LFP type battery is frequently used for house bank units because this chemistry has good stability, doesn’t use nickel or cobalt (which reduces cost) and is less prone to thermal runaway. LFPs also have long cycle life, with 3,000 cycles often quoted by battery makers.
When reached by phone on his Malo 46 Nada while cruising in Ireland, boat systems guru, author and cruiser Nigel Calder noted that LFP batteries have become popular installs on bigger boats. “That’s probably true when you look at the higher end,” Calder said. “Most [new build] catamarans have lithium-ion and they make sense for anyone with a high output alternator.”
According to Calder boat owners and marine insurance companies have two potential issues with lithium-ion batteries: cost and the idea that they are a potential fire risk. “Price has come down a bit,” Calder said. “They are currently running about $1,000 per kilowatt hour.” And he said that underwriters can be skittish about insuring boats with lithium batteries, even though that problem is overstated. “They are afraid of fires, they don’t know their research.”
The American Boat and Yacht Council (ABYC) has a lithium battery standard, E-13, which was most recently updated in 2022. This standard lays out requirements for proper installation of lithium-ion units larger than 600 watt hours. Even though the idea that lithium-ion batteries may be a greater fire risk seems to linger with voyagers and the insurance industry, Calder points to the need for manufacturers to follow good practices and for installers to follow E-13 ABYC standard. “There should be no problem if they are properly designed and tested,” Calder said.
Calder currently has 11 kilowatt hours of Torqeedo NMC batteries installed aboard Nada. He noted that in the past he spent considerable time overseeing the state of charge of his boat’s battery banks, but with Lithium-ion batteries and a powerful Integral charging system he does that far less often and has plenty of electrical power to run all the many electrical gear on the boat, including an induction stove, and an electric kettle for making frequent pots of tea. “It’s a game changer really. We don’t ever look at the battery state of charge any more.”
Calder’s experience highlights a key point about lithium-ion batteries: they are best for voyagers who demand the most from their boat’s battery banks. Ryan Ellison, who cruises aboard his Beneteau Oceanis 40 Polar Seal with his partner Sophie (they have a popular Youtube channel together called Ryan and Sophie Sailing) and who is also director of business development and co-founder of Dakota Lithium Batteries, reinforces the idea that boats regularly doing deep discharging of their battery banks will do better with lithium. “We had one season cruising with lead acid batteries,” Ellison said. According to Ellison changing to lithium batteries was a noticeable difference. “We’ve had lithium on our boat for four or five years and done three Atlantic crossings. For a cruising boat it’s the best way for energy storage. For daysailors it’s a little bit of overkill.”
Ellison admits that one of the big questions voyagers have about lithium-ion batteries is safety. He insists that lithium-ion units are safe but that it can take awhile to explain that to people, who associate LFP batteries with the higher performance lithium-ion chemistries that are used in car batteries and that have a bigger chance of thermal runaway. “LFP is still susceptible to thermal runaway,” Ellison said, “But it’s more difficult to get it to go into that state.”
Another issue is price, with LFP batteries having a higher price tag than comparable lead acid units. Ellison stresses that while the front end price is higher, LFP batteries have longer lifetimes and can be used for a greater number of life cycles. “When you do the math, it’s pretty comparable,” Ellison said. “The public is starting to understand and the changeover to lithium is happening.”
According to Denis Phares, founder and CEO of lithium-ion battery manufacturer Dragonfly Energy, which markets its batteries both under the Battleborn and the Dragonfly names, his company is working on a new type of solid state lithium-ion battery. “It will have a dry electrolyte powder,” Phares said. Without a liquid electrolyte, according to Phares, the probability of a fire is virtually eliminated. And even if there is a fire on the boat the solid state Dragonfly battery won’t burn and add to the fire. Phares said the dry process reduces the cost of manufacture of the battery, possibly leading to reduced cost to the boatowner. Phares said that by the first quarter of next year the company will start intensive development of this technology.
By October Dragonfly will start offering its Dragon Intelligence (DI) option on its battery line. The DI option will have built-in monitoring circuitry to provide info to a smartphone app that will inform users of battery health and the health of the battery management system.
Looking at the larger market for batteries, across the whole spectrum of marine battery use cases, how much are lithium-ion units changing things? Andrew Finkelstein, vice president of sales and technology at Lifeline Batteries, which sells both lead acid AGM and LFP marine batteries, says the overall market is not experiencing a massive shift to lithium-ion batteries. “It’s not changing as fast you might think. They’re making a foothold but AGMs still have a stronghold.” Finkelstein claimed the market is still 5,000 to one in the favor of lead acid units.
Finkelstein said the primary drawback of lithium-ion remains the price. “It’s a big step up,” he said. “If lithium was the same price people might do it. But most people won’t benefit from switching to lithium. Lead acid will be around for awhile.”
Still, Finkelstein points out that there are regular advances in battery technology by high capacity AGMs and by LFP units, which is only a good thing for voyagers. “It’s an exciting time for batteries.” n