Your boat’s cranking and house batteries are the nerve center of your entire cruising career. And our assumptions about what is best in power storage are rapidly being challenged by newer technologies that have matured from the experimental stage to stable systems that will serve our cruising needs over the long haul. Beyond the standard flooded, AGM and gel batteries, there are new approaches such as lithium-ion, fuel cells and the latest technological breakthrough — carbon foam batteries — that might change the way we design our vessels’ battery and charging systems.
The three standard battery technologies most offshore sailors know are flooded, absorbent glass mat (AGM) and gel. The old workhorse, the flooded battery, maintains its popularity through its low purchase price, resilience to charge voltage fluctuations and, as a starter battery, the capacity to provide a large jolt of cranking amperage without causing harm to the bank. On the downside, a flooded battery generally has a shorter life than a gel or AGM bank, and it generally does not accept a completely full charge. The other potential drawback is that it must be installed right side up since it is not sealed.
For the starter or main battery bank, a flooded battery is still a wise choice, but an AGM bank is also an option. AGM batteries are constructed of sandwiched boron-silicate mat, which keeps the electrolyte stable in any position except upside down. AGM batteries are spill proof, valve regulated and highly resistant to vibration. AGM units are also capable of accepting a charge much faster than flooded batteries, a key selling point when we consider the amount of fuel or time from a solar panel or wind generator to recharge a deep-cycle house bank. And whereas a flooded battery needs to have at least four times the capacity as the largest combined house load on a vessel, an AGM battery reduces the requirement to a ratio of 3 to 1.
Gel batteries are lead-acid banks just like flooded and AGM, except with an electrolyte composed of silica gel, which allows the battery to be installed in any position — even upside down. One key advantage of gel batteries is they can sit completely discharged for up to a month yet still accept a full charge. What’s more, they are highly resistant to overcharging and can keep a full charge for long periods in extreme cold.
On the flip side, these cold-loving batteries suffer from a dislike of excessive heat. Any gel battery installation should be away from the engine compartment in order to prevent an early death to this bank. Another limitation is their sensitivity to charging voltage. A cheap battery charger or an alternator not producing the exact voltage required by a gel battery will soon destroy the battery, which otherwise could last many years.
Lithium-ion batteries have come a long way from the early 1980s, when they were known for their instability and, in some highly publicized cases, spontaneous combustion and serious bodily injury. Now we take the safety of lithium-ion batteries for granted in our cellphones, laptop computers and other personal electronic devices. Today’s marine lithium-ion batteries pair up one or more anodic metals, such as manganese, with lithium as a cathode to produce deep-cycle batteries for house banks and electric outboard motors.
A Rolls Battery HT-8D is an example of a reliable, flooded cell lead-acid model long popular with voyagers.
Courtesy Rolls Battery
The chief advantages of lithium-ion batteries are the significantly lower weight (some can actually float) and the capacity to discharge and fully recharge hundreds of times over. Also, lithium-ion batteries can maintain a full charge for up to a year, adding substantially to their dependability and to their cost effectiveness for cruisers.
The stability of lithium-ion batteries is critically dependent on the purity of metals in the battery and the isolation of the batteries’ contents from impurities. A tiny crack in the battery casing could allow minute amounts of salt water, along with microscopic flecks of metal, to enter the battery’s core and start an unstoppable chain reaction resulting in an explosion or fire, the total destruction of your vessel and, ultimately, loss of life.
The solution to a lithium battery’s volatility is to isolate the cells into separate compartments, preventing extensive damage due to puncture. The OPE Li-3 lithium battery developed by Bruce Schwab, America’s first Vendee Globe finisher, in conjunction with Lithionics of Clearwater, Fla., contains nano-ceramic separators within each cell to enhance charge rates and to act as a “shut-down curtain” in the event of cell failure or penetration by a sharp object. Schwab claims a 100 percent safety record for the OPE Li-3 battery over the last four years — an impressive record for this new battery concept.
An added feature of the OPE Li-3 is a separate battery management system (BMS) module featuring “dual-channel battery management,” in which the charge side of the battery is isolated from the side leading to the switch panel. This configuration prevents a problem on one side from interfering with the other. Both channels have high and low cut-off points for charging. If the charge climbs too high or drops too low, the BMS automatically shuts off the battery, which cuts off all inputs to the bank, whether from the engine alternator, wind generator or other charging source. To resume supplying power to a load when the battery is overcharged, you simply press either the manual or remote reset button to bypass the shut-off.
Installing multiple banks on separate BMS units running in parallel offers ample reserve power while protecting each bank from the others. This improves the chances of having a functioning battery bank intact after a hit by lightning, which actually occurred to one of Schwab’s clients. “There’s strength in numbers,” he emphasized.
The OPE Li-3’s lithium-ion-iron-phosphate electrolyte offers six to eight times longer life and greater safety than flooded lead-acid batteries, and is “four to seven times lighter than any other battery” in a given size range. The OPE Li-3 battery line is available in eight sizes, from a 12-volt group 31 (G31EXT) to a 48-volt 9D (9DR).
A lithium-ion battery by Lithionics. This OPE-Li3 battery has a “dual-channel” controller unit in which the charge side is isolated from the load side.
The sticker price of a lithium-ion battery can be five times as much as an AGM battery of similar amp-hours, and more than 10 times the cost of a flooded deep-cycle of the same amp-hour rating. However, if we consider the longer life, greater cycling resistance and new safety features of the OPE Li-3, the cost over its lifetime is less than that of a flooded battery.
A new twist in an old technology is Firefly Energy’s Oasis Group 31 carbon foam battery, built around carbon foam plates containing a small amount of lead within an AGM structure. This groundbreaking advancement in battery design severely reduces sulfation on the plates while tripling the number of cycles capable in the unit. The carbon foam construction permits discharges of up to 100 percent of rated capacity without any loss of performance — a claim unheard of in traditional flooded batteries.
The Firefly Group 31 rates about equal to a standard AGM 31 in terms of amp-hours (101-116), but somewhat higher in reserve minutes — 225 amp-hours versus the 200 amp-hours associated with standard group 31 banks.
Sailing guru and nautical author Nigel Calder tested a set of Firefly Group 31 batteries during a two-month cruise off the west coast of Scotland and was highly impressed by the results of this new carbon foam AGM platform.
“The kind of operating regime I followed spells death for most lead-acid batteries,” explained Calder. “In contrast, after two months of intensive cycling, the Firefly batteries tested out with 100 percent of the capacity with which they started.”
Hydrogen fuel cells are another battery technology attracting a lot of attention among ocean cruisers. Rather than receiving a charge from an alternator or other power source, a fuel cell combines hydrogen and oxygen within what is called an “electrochemical energy conversion device,” which continuously produces electrical power in the process.
Traditional lead-acid batteries have metal grids that hold active soft lead material. A carbon foam plate uses a material with a large surface area.
In a fuel cell, hydrogen forms the positive cathode, and oxygen from the surrounding air forms the negative anode, unlike in a conventional battery with its dissimilar metals submerged in an acid solution. A solid membrane serves as the electrolyte as power is collected at the positive and negative plates within each cell. As long as hydrogen and oxygen are introduced steadily to produce the chemical reactions essential to creating electrical power, the “battery” never wears out. In its most common form, it produces a steady stream of water as its exhaust while producing electricity.
This all sounds wonderful, except that compressed hydrogen is both highly expensive and potentially dangerous, as hydrogen is extremely explosive. Fortunately, by storing hydrogen in a solid or liquid form, this volatile substance can be used safely to power a fuel cell, which can take the place of an alternator in charging batteries.
Harnessing hydrogen and turning it into a practical, simple electric generating system is what Dynad International has achieved with its Hydromax 150 fuel cell. Two plastic tanks of powdered chemicals — one with malic acid from apples, the other with salt — produce hydrogen on demand, and the fuel cell dispenses the spent HydroFuel, which is harmless and may be disposed of in any sewage system. An integrated voltage regulator controls battery charge by combining the chemicals as needed to keep batteries topped off.
The Hydromax 150’s main unit weighs a mere 20 pounds yet is capable of silently and consistently generating 12 volts at 360 amp-hours per day, as long as it has fuel. Hydrovane of British Colombia, makers of the Hydrovane self-steering system, is the North American distributor for the Hydromax 150 fuel cell system.
An alternate form of fuel cell technology is found in the Efoy Comfort, a user-friendly fuel cell generator gaining popularity among offshore sailors. This system is packaged in a self-contained unit much like the Hydromax but uses methanol, or wood alcohol, as its source of hydrogen. The fuel, packed in Efoy’s M10 fuel cartridge, emits harmless carbon dioxide gas during use. One 18.5-pound, 2.64-gallon fuel cartridge will produce approximately 11 kilowatt-hours of power; the life span of the cartridge depends on the amount of current drawn over time.
The 12-volt Efoy is available in three sizes, labeled by their approximate amp-hour days: models 80, 140 and 210. Offshore racer and 2010 Route du Rhum winner Andrea Mura installed an Efoy Comfort 210 fuel cell to provide auxiliary power aboard his Open 50 Vento di Sardegna during the Two Handed Transatlantic Race (“TWOSTAR”) 2012.
The Hydromax 150 is a fuel cell unit that uses two powdered chemicals to produce hydrogen gas, which is then combined with the oxygen in the air to produce power.
Easily charged fuel cells open up the possibility of eliminating diesel and gas auxiliary engines from sailing craft altogether, leaving the engine box to a small electric motor producing the same rpm and horsepower as its gas or diesel predecessor. Fuel cells could keep our battery banks perennially charged, powering every electric device on our vessels, including the refrigerator and autopilot. For the foreseeable future, though, most of us will continue to include a diesel engine in the mix to charge our battery banks and provide main propulsion power.
When considering the various battery types available to us, it is tempting to optimize each battery selection, including the particular type of battery, for a particular set of tasks. This is okay, but with one great caveat: Avoid turning the battery selector switch to ALL while running the engine if the batteries are of dissimilar types, unless you are using a smart controller capable of detecting different battery charges separately and automatically shifting charging current to the battery in most need. Flooded, AGM, gel, lithium and the new carbon foam batteries have different charging times, temperatures and flow curves from bulk to taper to float charge. By charging all at the same time, you risk over- or undercharging at least one of the banks and possibly damaging them.
For the starter motor bank, the best bet is to adhere to the engine manufacturer’s specifications regarding group and cranking amps. This one battery, with its singular purpose to provide a quick burst of energy to turn over a high-compression diesel engine while powering an electric fuel pump and a set of glow plugs, is almost always a traditional flooded group 24 or 27 battery. New developments in AGM batteries, though, have proven this to be a sound alternative technology for starter batteries, not just dual-purpose house banks.
AGM cranking batteries are available from several manufacturers and are the preference of sailors who do not mind paying a little extra for what these batteries offer: low discharge rates, resistance to vibration, safety from acid spills and versatility in installation. Lifeline, Mastervolt and NorthStar are just a few of the companies offering standard AGM starter batteries.
NorthStar’s thin-plate pure lead AGM batteries are in a category of their own. These cranking batteries offer an astounding amount of initial power: Their smallest battery, the group 24, produces 840 cold cranking amps, beating or matching any other battery of is size. This battery offers 160 minutes of reserve power and, like all AGM batteries, shorter recharging time than flooded batteries along with zero maintenance. AGM batteries are typically, although not always, higher priced than flooded batteries of the same size, so be prepared to shell out at least three times the price of a flooded battery for a top-of-the-line battery in its class.
After all, if we can produce enough power with solar panels, a wind generator, a hydro generator and a fuel cell to top off house batteries and run an electric propulsion motor, who needs a diesel engine?
Bill Morris is the author of Sun, Wind and Water: The Essential Guide to the Energy Efficient Cruising Boat, published by Seaworthy Publications.