Lead-Acid Battery Technology Modernizes for Maritime Operations

Lead-acid batteries have existed for over a century with little change. Advances have occurred in lead-acid battery technology to increase storage density, extend usable service life and improve cold weather performance at comparatively lower cost than modern battery technologies. As a result, derivatives of lead-acid battery technology still have multiple applications in modern boating.

The history of lead-acid batteries goes back prior to World War I, when battery-powered passenger vehicles traveled along the public roads. Designers of submarines that operated during both WWI and WWII installed banks of batteries to provide low-speed propulsion over short-distances when the vessel traveled submerged. During later years, a segment of the fishing industry that operated low-speed trolling vessels often used lead-acid batteries to provide vessel propulsion. The batteries also found application in mining locomotives, small industrial locomotives as well as in multi-stop post office and dairy delivery vehicles.

While built in a variety of sizes, the essential chemistry involving plates of lead and sulfuric acid remained unchanged for decades. Lead-acid batteries are temperature sensitive, providing optimal performance between 10-deg C (50-deg F) and 50-deg C (110-deg F). At minus 25-deg C (-15-deg F), the battery will typically deliver 20% of the power that it would deliver at 25-deg C (75-deg F). Repeated deep-discharge from 100% to below 10% of storage capacity greatly reduces service life expectancy. Sulfur build-up on lead plates reduces storage capacity while fully drained batteries often cannot be recharged. 

Improvements

Several initiatives were undertaken during the latter part of the 20th century to improve the performance of lead-acid batteries. One approach involved adding small amounts of other chemicals into the sulfuric acid to improve performance at low temperatures. Another approach involved mixing a large proportion of silicon dioxide with the sulfuric acid, except that at the time it reduced battery voltage. The AGM or absorption glass mat approach led to the development of the spiral cell, where plates of lead and lead-oxide separated by the glass mat were rolled into a spiral to increase storage capacity. 

Early researchers abandoned the silicon dioxide method, being unable to increase voltage. Many years later, chemists revived the concept and revised the battery chemistry with 5% sulfuric acid and up to 95% silicon dioxide. The revised electrolytic mixture proved capable of operation at minus 40-degrees on either scale, delivering 60% of the power that it delivered at plus 50-deg C (110-degF). The tiny amount of sulfur in the battery greatly increased usable service life by reducing build-up of sulfur on the lead plates, allowing over 2,500-recharges when drained from 100% to just above 50% of storage capacity.

The Engine Company

The United States EPA mandated that fumes from combustion engine crank cases be circulated to the engine intake, for combustion. However, positive crank case ventilation resulted in formation of carbon deposits on engine valves. Efforts at dealing with the problem of hardened carbon deposits led to the discovery that the carbon deposits mimic lead plates when exposed to sulfuric acid and an electrical charge. The discovery led to the development of the carbon foam battery where blocks of carbon replace the lead plates in what is essentially a modified lead-acid battery.

The carbon foam is porous and offers equivalent electric storage capacity of a much larger lead plate, while being resistant to build-up of sulfur deposits that is problematic with lead. It offers the combination of much higher storage capacity than a lead-acid battery of equivalent size and weight, with greatly extended usable service life when repeatedly operated between 100% and just over 50% of storage capacity. There are numerous applications where carbon foam batteries can replace lithium batteries that incur double to 3-times the capital cost while offering only slightly higher energy storage capacity.

Boat Operation

While most operation of small boats occurs in warm weather, a small number of boats continue to operate during colder weather. When air temperature drops to the freezing point of water, salty seawater remains liquid and especially when waves, tidal currents and ocean currents are present. At such temperatures, flowing river water also remains liquid and allows for boat navigation. The lead plated battery that contains 5% sulfuric acid and 95% silicon dioxide is also dubbed the lead-crystal battery and easily sustains the operation of battery-powered, low-speed, short-distance boats during cold weather.

Lead-crystal batteries cost 1/3rd as much as lithium batteries and can deliver over 2,500-cycles of service when repeatedly operated at 50% depth of discharge. At 50% the cost of lithium batteries, the carbon foam battery is currently only available with sulfuric acid electrolyte and can deliver over 3,500-cycles at 50% depth of discharge and over 1,000-cycles at 80% depth of discharge. It can deliver over 65% of its rated power at sub-freezing temperatures as low as 0-degrees F. Other than propulsion, these batteries can fulfill a wide range of other applications on small boats powered by internal combustion engines.

Starting Cold Engines

At sub-freezing temperatures, flowing water remains liquid while stagnant water solidifies. Flowing water and especially flowing seawater driven by ocean current and by changing tides allows ports such as New York City, Newark, Halifax, Quebec City and Montreal to remain operational during sub-freezing winter weather. Commercial truck size internal combustion (IC) engines are often installed into tug boats, fishing boats, ferry boats and port area vessels. Sub-freezing weather often causes difficulty in restarting cold IC engines. In such situations, deep-cycle batteries capable of operating at sub-freezing temperatures become especially useful.

Both lead-crystal and carbon foam batteries can sustain several hours of operation of engine heaters that require battery power to operate a water pump and combustion of a small amount of hydrocarbon fuel. Prior to engine starting, these batteries can also sustain operation of electric oil pumps that pre-lubricate the IC engine. It will then recharge an ultra-capacitor that will dump high starting current into the engine electric starter motor, before blending in to maintain engine cranking prior to ignition. Battery power can also recharge a new spring-loaded engine cranking technology to initially turn over the engine. 

Port Service Vehicles

Both the lead-crystal and carbon foam batteries have potential application in a variety of port service vehicles. Fork-lift trucks and container picker trucks require considerable counter-weight, enhancing the suitability of banks of heavy lead-based batteries for such service at smaller ports. Some smaller ports use industrial-type battery-electric locomotives for short-haul shunting service. Both lead-crystal and carbon foam battery technologies offer superior cold weather performance than traditional lead-acid batteries, allowing for shunting operations with air temperature at 0-deg F (-18-deg C), when either battery would offer over 65% of energy availability compared to 70-deg F.

There are northern ports such as Montreal that remain operational during the northern winter month and including when air temperatures drop to well below the freezing point of water. At such low temperatures, the performance of some lithium batteries becomes problematic, including incurring difficulty recharging. The lead-crystal battery and carbon foam battery both remain operational at 0-degrees F, with the possibility of a hybrid carbon foam and silicon dioxide battery technology having application during severe winter service.