These days, the battery universe is in a constant state of movement, with the driving force coming from the lithium-ion world. It seems that almost monthly, some lithium-ion battery manufacturer announces improvements in energy density, cycle life or other key determinants in marine installations. These advancements, in turn, are forcing a considerable amount of development in the absorbed glass mat (AGM) lead-acid industry to blunt the penetration of lithium-ion batteries into traditional lead-acid marketplaces.
In the lithium-ion world, two chemistries currently predominate: nickel manganese cobalt (NMC), used primarily by Torqeedo and lesser-known brands such as Volta, and lithium iron phosphate (LFP), used by pretty much everybody else. NMC technology inherently has higher energy density (more stored energy for a given volume and weight), and LFP technology has a higher cycle life, but these are, to some extent, moving targets. For example, the energy density of both chemistries is steadily increasing, so LFP from one manufacturer can sometimes leapfrog NMC from another.
There has been adverse publicity with respect to lithium-ion fire risk, so let’s address this issue head-on. All lithium-ion batteries in the marine marketplace have a flammable electrolyte. Given certain fault conditions, NMC can generate sufficient internal heat to set itself on fire, whereas LFP cannot, but this is to some extent a false distinction. Given the kind of fault condition that leads to “thermal runaway” and internal heating, LFP chemistry will not spontaneously combust, but it will build pressure that is likely to burst cases and create internal short circuits. If this pressure generates a spark, the electrolyte is likely to ignite.
With both chemistries, the key to a long-term, safe installation is a battery management system that pretty much guarantees that fault conditions will be detected and arrested before thermal runaway can initiate. From my perspective, the robustness of the battery management system is the key factor in determining battery suitability for marine applications. Should the system nevertheless fail to prevent a thermal runaway event, some batteries are designed to contain a thermal event within the battery case.
A considerable number of Underwriters Laboratories and other standards can be used to test batteries for their ability to handle, and safely contain, a variety of fault and abuse conditions. By far the most rigorous of which I am aware is UL 1973. I would not hesitate to put any battery that is UL 1973-certified in my boat. However, testing to these tough standards can be extremely expensive, so it is rarely done.
My fallback position is to only use batteries from well-established marine brands. They likely will have taken steps to ensure the appropriateness of their batteries and management systems for marine applications. I frequently advise against buying from companies that have neither third-party abuse testing conducted by recognized test laboratories nor an established marine track record.
What about lead-acid technology? It has long been known that we are only unlocking a fraction of the theoretical capacity of lead-acid batteries. A decade or more ago, it was discovered that adding carbon in various forms, especially to the negative plates, can improve performance — notably, the resistance to sulfation (probably the No. 1 killer of batteries in boats) — and can increase cycle life.
The most advanced form of carbon utilization is found in Firefly AGM batteries, which are almost immune to sulfation, with excellent charge acceptance rates and a high cycle life. This is a terrific technology for which Firefly owns the patents. Other AGM manufacturers have added carbon to the active material in their negative plates, with improvements in resistance to sulfation. Notable in the marine space is Northstar.
East Penn has the rights to a different carbon approach in which a carbon plate is added to the negative plate. This process has the effect of creating a capacitor. Capacitors can absorb huge energy spikes but cannot store much energy. The idea here is to be able to capture the potentially massive energy spike when a hybrid automobile is braked, then feed this energy back into the battery to be stored. It remains to be seen if this technology has any relevance in the marine world.
Finally, there is the Betta lead-crystal battery, which is a newcomer. Bruce Schwab at OceanPlanet Energy has done some limited testing that shows promise, but it is way too early to render judgment.
Almost all of this lead-acid development has been done empirically: A change is made to a battery, and it is tested to see what effect the change has. In contrast, we now have a joint research effort between a number of U.S.-based AGM manufacturers and the Argonne National Laboratory in Illinois to try to understand the fundamental physical, chemical and electrical processes taking place inside lead-acid batteries.
If this project can unlock the science, we are likely to see substantial improvements in performance. Given the considerable price advantage that lead-acid holds over lithium-ion, improvements will help head off the competition.
If the Advanced Lead Acid Battery Consortium and Argonne National investigations achieve anywhere near their targets, we should see significant improvements in lead-acid batteries in five or so years. Lithium-ion will see incremental improvements in energy density and other features.
And some other technology may come out of left field. All kinds of research is underway on multiple fronts, but, if successful, the results would take several years to filter down to users.
Nigel Calder is the author of the Boatowner’s Mechanical and Electrical Manual, among other marine titles, and is a longtime member of the ABYC’s Electrical Project Technical Committee.
This article originally appeared in the November 2019 issue.
