Lithium-ion battery safety for boaters

Dwight Bues


Ubiquitous in everyday life, lithium-ion (Li-ion) batteries power weed trimmers, leaf blowers, chainsaws, drills, impact wrenches, and other cordless tools. Ten years ago, these tools used nickel-cadmium (Ni-Cd) or nickel-metal hydride (Ni-MH) batteries. The transition has been swift. Now that Li-ion batteries have recently entered the recreational boating industry, what safety precautions do we need to consider when using them?

How Li-ion batteries work

A Li-ion battery’s utility relates mainly to its energy density. Back in the 1970s, zinc-air batteries were touted as having great power-to-weight, though they were only primary batteries (not rechargeable). Sodium-sulfur batteries had a great power-to-weight ratio as well, but their hot 400-degree electrolyte made them dangerous.

According to a report by ION Energy, a typical Li-ion battery stores 150 watt-hours of electricity per kilogram, whereas a lead-acid battery stores just 25 watt-hours per kilogram.1 Li-ion batteries have been touted as having improved power-to-weight and smaller size and, while there are several vendors available to the boater, some specifications would help to illustrate. A Li-ion replacement for a class 8D absorbent glass mat (AGM) lead-acid battery has the same amp-hour capacity in one-third of the weight. Additionally, this Li-ion replacement is two-thirds the size of the class 8D AGM lead-acid battery.

Keeping this in mind, what future applications might this imply for the average boater? The most obvious near-term application would be to employ larger banks of house batteries, which would obviate the need for an auxiliary engine-driven generator. Once the technology is more mature, we could see a further 50% reduction in the batteries’ size and weight. Once this happens, full electric-only cruising becomes possible. (When a diesel propulsion engine costs $60,000 to $80,000, you could buy a lot of batteries with that.)

In the near term, a practical step would be an electric drive with one auxiliary-driven power plant. Twin screws give you great advantages in docking, especially in inclement conditions. Given the current advances in electric vehicle technology, it would be simpler and less expensive to have twin electric drives rather than twin propulsion engines, as well as far more efficient for cruising fuel economy.

Safety concerns for boaters

If you intend to use Li-ion batteries, you should understand the safety basics. As with AGM or other non-flooded-cell lead-acid batteries, you must use the appropriate charger. The referenced document from the Massachusetts Institute of Technology discusses mischarging as a key danger.2 Additionally, high temperatures can cause Li-ion batteries to deteriorate more quickly, making them more prone to spontaneous combustion.1

Li-ion batteries store lots of energy, which is why we use them. But they can overheat if stored improperly. A UPS cargo plane crash was caused by overheating.3 Shock and vibration may accelerate the deterioration of the cells. The investigation into the Boeing 787 fires determined that Li-ion batteries may need more isolation and padding of the cells within the battery to prevent shock and vibration problems and mitigate “thermal runaway,” when a battery enters an uncontrollable, self-heating state.4 Given how batteries are classically installed in boats, it might be a good idea to provide a solid rack mount for Li-ion batteries. Additionally, we need to figure out a better idea than sticking them low in the bilge.

Li-ion battery fires can be difficult to extinguish. Experience has shown that the correct way to extinguish a fire is to use a Class-BC fire extinguisher or lots of water.5 Since there is no metallic lithium present, you should not use a Class-D fire extinguisher.6

While it’s a little scary to analyze worst-case scenarios, knowledge of the mechanics of Li-ion battery failures helps us to prevent similar occurrences. One commonality in Li-ion battery failures is that overheating of one cell can cause thermal runaway in multiple cells. The example of the Boeing 787 battery fires illustrates this case.7 It’s also understood that their compact packaging may make the problem worse.

A common Li-ion cell contains its own oxidizer, so using the fire model that USPS teaches for fire extinguisher use, you cannot remove “air” from the three-legged fire triangle (air, fuel, heat). What’s more, the Li-ion cell contains its own fuel, as the electrolytes can be flammable. While chemical foam will extinguish the fire, it could flare back up. Toxic smoke and ejected electrolyte pose additional dangers.

In the wake of Hurricane Ian, Tesla owners discovered, much to their chagrin, that intrusion of salt water into the electrolyte can short-circuit a Li-ion battery enough to cause a fire. Many of these fires happened days after immersion.8 For this reason, the common practice of installing batteries way low in the bilge must be reconsidered when it comes to Li-ion batteries.

I believe that future uses of lithium-ion batteries can enhance our boating experience, but we must be sure to follow all safety considerations during the design, implementation and maintenance of our marine electrical systems.


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Dwight F. Bues

Dwight Bues is a member of America’s Boating Club Northern Virginia/5 and a member of the national Boat Systems Committee.

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