Is it time to power up with lithium?
Outboard engine manufacturers are constantly introducing newer and bigger internal combustion power-plants like the Suzuki DF350, the Yamaha F425, and the Mercury 600 Verado, which push past the existing limits one after the next. Meanwhile, automotive manufacturers are moving in the diametric opposite direction, producing more and more all-electric packages with motors that are intertwined with digital controls, touchscreen interfaces, and powered by whopping-big batteries. There’s no question which seems more technologically advanced, and the marine industry tends to lag at least five years behind automotive, but it begs the question: why aren’t more mariners taking advantage of the latest and greatest in batteries?
The answer: a few early adopters are already doing so, but since most marine propulsion systems are destined to remain fossil fuel dependent for some time to come, the benefits of better batteries remain relatively peripheral for boaters. And as for boats going all-electric, don’t hold your breath. But… there’s a big “but.”
Fossil Fuel Vs. Batteries
The problem with all-electric boats lies in energy density and basic chemistry. Gravimetric energy density (the energy per mass of any fuel) is measured in megajoules per kilogram (MJ/kg). A megajoule is a million joules, one joule being the force of one newton acting through a distance of one meter, which is considered the international standard for measurement of energy. Gasoline can hold around 46 MJ/kg. A lead-acid battery can only swing a meager 0.14 MJ/kg. So every pound of gasoline you haul around can produce well over 300 times as much energy as every pound of conventional-tech battery. The newer LiFePO4 batteries (basically, lithium-ion batteries with iron phosphate cathodes that don’t blow up the way some older lithium batteries did) do a lot better than lead-acid, packing away up to 0.7 MJ/kg. Still, obviously, that’s way less power than burning dinosaurs can provide.
The reason for this disparity? Organic chemicals such as gasoline, butane, or even carbohydrates, can store a lot more chemical potential energy than we’re able to cram into a manmade power cell of equal size. For example, a roast beef sandwich has an energy density of about 11 MJ/kg, almost 16 times the grunt lithium-ion can provide. Unless you’re planning on rowing your boat you probably don’t care about the viability of sandwich-powered propulsion, but it shows how much potential energy is locked inside organic material versus our best attempts to artificially store energy in a box. Mother Nature not only wins, she kicks human butt in a big way.
If you do your fishing from a boat small enough that you could, in fact, power it with a roast beef sandwich and a pair of oars, the latest and greatest electric outboards with integrated LiFePO4 batteries may be of interest to you. But these top out at around 10-hp. Bigger motors require bigger batteries, and while a few boats with electric outboards up to 80-hp have been built, they still can’t offer ranges at cruising speeds suitable for most serious anglers. So, when you’re talking about more substantial fishing boats, at least for the near-term all-electric rigs are still a thing of the future. That leaves only starting and house battery banks and electric trolling motor power systems in play.
LiFePO4 to the Fore
Your average mid- to upper-20-something center console will have between two and four lead-acids in it, the biggest downside to those batteries being weight, usually somewhere between 100 and 200 pounds in total. Now let’s say the boat has a 36-volt electric trolling motor on the bow. Add in another 150 pounds, which will need to be stored relatively far forward. On a boat of this size, were talking about enough weight that it can affect running characteristics and speeds.
Switch to LiFePO4 and as a general rule of thumb you can cut weight by about two-thirds, so a complete switch could cut weight overall by up to 200 pounds. Except that you could cut it even more, because lithiums deliver 30- to 40-percent more useable energy for their amp-hour rating. So, you can replace a 100 amp-hour lead-acid with an 80 amp-hour LiFePO4 and actually gain on run-time. Plus, lithium batteries have much longer life spans and most can cycle thousands of times versus hundreds of times for lead-acid.
Wait a sec — I know what you’re thinking: “But, those LiFePO4 batteries cost a whole heck of a lot more then lead-acid. Is it really worth it to make the switch?” In a nutshell, yes. The critical factor here is the extended lifespan we just mentioned. Depending on the specific batteries you’re talking about and who’s numbers you believe, the average cost per kilowatt hour over the full lifespan of a lead-acid batters runs at around $0.70 to $0.75. But for a LiFePO4 and all those extra years of service, it shakes out closer to $0.20 to $0.30.
Wait a sec, again — there can be additional costs to converting to lithium. These batteries require battery management systems (BMS) to regulate charging in very specific ways, and you can’t just hook them up where your lead-acids used to be and expect all to be well. Every system is going to be a bit different, just know that this is more of a system conversion than a battery replacement and additional costs are likely to be involved. As a point of reference, we’ll note that a BMS for a simple 12-V alternator/starting battery costs around $200, and a full-on system with Bluetooth connectivity and the capability to handling inverters, batteries in parallel, etc., goes for more like $1,000.
The Bottom Line on Batteries
When you get down to brass tacks, what you and I want is to step onto our boat, have the engines crank right up, have the electronics work properly from the moment we leave to the moment we get back, and get power to all the other systems and accessories whenever we want. For many of us with reliable systems we’re happy with, the smart thing may be to leave it well enough alone. And at least for the time being, getting fully integrated all-electric systems simply isn’t in the cards unless you’re okay with speed and range that are lake-worthy, at best. But if you’re having a new boat built or significantly refitting an older boat, the advantages of LiFePO4 are just too big to ignore — especially if you don’t have any roast beef sandwiches in the cooler.