Lithium-Ion Batteries: Handle With Care

Photo: Nigel Calder

Who wouldn't want a battery one-quarter the weight and size of their current lead-acid battery but with comparable energy storage capacity? Most of us have grown comfortable with the lithium-ion (Li-ion) batteries in our smartphones and laptops, so it's natural to assume they will work in cars, on aircraft, and in our boats. Unfortunately, safely scaling up these compact, energy-dense batteries to the much larger sizes needed to meet heavy-duty energy demands is not straightforward. In addition, the technology is still developing, and there are already enough types of Li-ion batteries to tonguetie a chemical engineer: lithium iron phosphate, lithium manganese oxide, and lithium nickel manganese cobalt, to name a few. Each has its own voltage, energy density, and safety characteristics. Before getting lost in the details of these competing chemistries, any boater considering installing Li-ion batteries on their vessel needs to understand the risks and the costs, not just the benefits.

Li-ion Battery Challenges

Unlike conventional batteries, when Li-ion batteries fail, they can do so catastrophically. Here's the problem: When an individual Li-ion cell gets overcharged, it gets hot. This can initiate a process of self-heating that causes the cell temperature to continue to rise even if the cell is taken off charge — something known as thermal runaway. Once started, thermal runaway is difficult to stop. Depending on the battery chemistry, the cell may get hot enough to spontaneously catch fire.

It gets worse: If a single cell enters thermal runaway, it begins to overheat its neighbor, which overheats the next one, and so on. This can cause a cascading failure that results in the battery burning uncontrollably. Even if a cell that has entered thermal runaway does not get hot enough to catch fire, it can swell up and rupture, venting the flammable electrolyte.

The potential for thermal runaway with any Li-ion battery chemistry means that when installing them on boats, they aren't plug-and-play. They charge at different voltages than lead-acid batteries do, and simply connecting them to a conventional charger is asking for trouble. To keep their concentrated power in check, Li-ion batteries rely on a sophisticated management system that actually tracks and balances the voltage differences between each cell, unlike the monitoring systems used with lead-acid batteries that simply show you what's going on. Among other things, proper management systems also contain over-voltage and short-circuit protection. Unfortunately, these management systems are vulnerable to lightning strikes or power surges, and any failure in the system can lead to a fire. While some Li-ion chemistries may be more resistant to thermal runaway than others, if you mismatch a charging system or choose the wrong battery management system, you could still find yourself with a charred hull. That's why the design and installation of Li-ion battery systems are best left to professionals.

If the potential dangers of Li-ion batteries are not enough to convince a hopeful early adopter to wait for the technology to mature, the price almost certainly will. A single replacement house battery will set you back around $2,000, and that's before the battery management system and the upgrades to alternators, battery chargers, and voltage regulators.

The Future of Li-ion Batteries

Li-ion batteries have a bit in common with propane tanks: They're a high-energy storage system that is potentially dangerous. Fortunately, with propane, we (usually) manage to avoid disaster. But propane systems have a complete set of American Boat and Yacht Council (ABYC) safety standards that govern their installation and use. While the ABYC is closely following developments, Li-ion batteries are an evolving technology, one that the aircraft and auto industries still haven't perfected. Until the market narrows down to one or two chemistries and reliable, robust battery management systems, it's all but impossible to develop standards for the safe installation and use of Li-ion batteries on boats.

While Li-ion batteries may just revolutionize heavy-duty energy storage someday, the costs and risks still outweigh the benefits for most recreational boats. Until more data exist on which type of Li-ion batteries work best for boats, and what unexpected issues may arise, Seaworthy recommends that most boaters steer clear of these compact, high-energy batteries. For the few boats where the benefits of Li-ion batteries might outweigh the expense and the risks, such as offshore racing sailboats and tournament bass boats, we recommend that the systems be professionally installed and professionally maintained.