Lessons Learned - April 2019

Marine Batteries

I do not think that a week goes by that I do not get a call from someone with battery issues of some sort. I have seen everything from flooded electrolyte batteries that have been ignored for months or years and finally exploded, to batteries that were literally so dead that they were nothing more than ballast. Depending on the systems on your vessel there may be anywhere from only one battery that does it all to a dozen more, each with a particular purpose. A mid-size cruiser today will generally have a dedicated starting battery for each engine, one for the generator, one or several for house systems, one or more for the bow thruster and some for the stern thruster. In addition if you have an inverter there is likely a dedicated bank for that system as well. It is not uncommon to see seven or eight batteries on a 40-foot motoryacht.

Some batteries require regular maintenance with checking and adding water at least monthly but the price premium for maintenance free batteries is so small today that it does not make sense to not go for the upgrade.

Battery Basics

The flooded electrolyte lead acid battery was developed in the mid 1800′s and has remained basically the same until the 1970′s when the sealed lead acid, SLA for short, battery was developed. The basic construction of the lead acid battery has two lead lattices filled with lead oxide and pressed into a flat sheet. These plates are stacked together with a separator between the positive and negative plates and then immersed in a solution of 35% sulfuric acid and 65% water. The plates in modern batteries are not made of pure lead but have various amounts of antimony, tin, calcium, and selenium added to improve battery life, mechanical strength or to lower the cost of production. The use of these alloys is where manufacturers develop batteries for specific applications such as starting, deep discharge, traction, or low temperature performance.

There are two basic types of lead acid batteries and three subgroups. The two main types are starting and deep cycle. The three subgroups are the wet cell, the gel cell, and the absorbed glass mat. The starting battery is designed to deliver quick bursts of energy such as starting engines or powering a side thruster and they are constructed with more internal plates which are thinner and have a somewhat different material composition to optimize for high current loads. The deep cycle battery has less instant energy, but greater long-term energy delivery. Deep cycle batteries have thicker plates and the alloys added are designed so that the battery can survive a high number of discharge cycles. Starting batteries should not be used for deep cycle applications because the thinner plates are more prone to warping and pitting when deeply discharged. The dual purpose battery is a compromise between the two types of batteries, though it is better to use batteries designed for specific applications where possible in marine applications that is generally not possible.

All flooded electrolyte batteries will generate oxygen and hydrogen gas from the water during the recharge cycle and with non-sealed construction this gas is lost from the battery. Periodic maintenance is required to replenish any water that has been lost. If maintained properly and recharged correctly, the flooded electrolyte battery can be expected to last two to three years in the marine environment. The newer Sealed Lead Acid or SLA battery is just that, sealed. Additional electrolyte is added at the time of manufacture, the battery case is sealed, and a safety valve is added. Over the life of the battery there is no need for inspection since no water can be added. Inside the battery there is a catalytic recumbent material that recombines any hydrogen and oxygen gas produced during recharge. The valve allows excess gasses to be vented in the case of high internal pressure when overcharged. These sealed batteries also have the advantage that they cannot spill their electrolyte if tipped over. The SLA battery has an expected life in the marine application of three to four years and is only slightly more costly than the non sealed counterpart.

Some lead acid batteries designed for applications where the battery can be mounted in any position use a gelled electrolyte. In this construction the sulfuric acid is mixed with silica creating a gel like material that will not flow. Because of the chemistry the gelled electrolyte battery has better low temperature performance and better resistance to shock and vibration. But with a cost premium of 3 to 4 times that of the SLA battery, and being very sensitive to recharge voltages, the gel cells are not common in marine or automotive applications.

Until recently the most modern and king of the hill in the lead acid battery family is the Absorbed Glass Mat Valve Regulated Sealed Lead Acid battery, commonly referred to as the AGM battery. These batteries have a similar design to the flooded electrolyte battery but have a separator made from a mat of glass fibers that holds the electrolyte. The plates in the AGM battery can be any shape; flat, bent, or even rolled. These batteries are the highest cost to manufacture, roughly 2 times the flooded electrolyte battery, but have many attractive features for the marine application. Mounting in any position as they are completely spill proof, no gassing during normal charging and discharging, no inspection or maintenance, operation in high vibration and high temperature environments, and an 8- to 10-year expected life. AGM batteries also have the advantage of a very low self discharge rate. SLA batteries will self discharge at around 15% of capacity per month while the self discharge rate of an AGM battery is less than 3% per month. There is no need to leave a charger connected to the AGM battery if not intended to be used for long periods of time. Even after one year of non-use, the AGM battery can be put back into service immediately with approximately 70% of original capacity.

The latest development of lead acid battery design is the Carbon Foam AGM. The main improvements that the Carbon Foam construction offers is greater resistance to sulfating and corrosion and an increase to the surface area of the battery plates. Sulfating is what limits the life of any lead acid battery and while the standard AGM excels at limiting it, further reduction over the current AGM design would extend the life beyond the now 10 years. The Achilles heel to the lead acid battery is that if it is stored for long periods of time with a partial charge, the plates will sulfate and capacity will be permanently lost. The carbon foam battery claims to eliminate sulfation of a partially charged battery thereby extending the life and capacity.

Another claimed benefit of the carbon foam battery is deep discharges of up to 100% are allowed and will not shorten the life or reduce the capacity. Discharging a conventional AGM battery to greater than 80% will severely shorten its life and has an expected charge/discharge amount of 500 cycles. The final claim of the carbon foam design is that it has improved low temperature performance over any other lead acid construction with a full operating temperature range of -20 degrees Celsius to +50 degrees Celsius. The price premium for the carbon foam AGM over a traditional AGM is pretty small making it potentially a good choice when replacement time arrives. My only hesitation is that the technology is new and I have seen only one manufacturer making marine batteries with this technology.

Starting Batteries VS Dual Purpose Batteries

Marine and automotive batteries are not designed the same and have several major differences. Batteries designed for automotive applications do one thing, start the engine. Once the engine is running the alternator recharges the battery and powers the car′s electrical system. It is a simple starting battery providing high currents for very short periods of time.

A marine battery is designed to both start an engine and provide power for other boat systems. It needs to provide short bursts of high currents for starting and also provide small amounts of current in a deep cycle for long periods to power the boat systems. In short, the marine battery needs to do two things at once, hence we refer to them as dual purpose.

To illustrate the differences battery manufacturers use terms like Cold Cranking Amps, CCA, to show the maximum instantaneous discharge current a starting battery can provide. Instead of CCA measure, a marine battery will be rated as Marine Cranking Amps, MCA, which measures the maximum current available at 0 degrees Celsius for 30 seconds, a much more realistic measure for the marine environment than the CCA rating of -20 degrees Celsius for 30 seconds. The deep cycle rating, in Amp Hours, measures the amount of current that the battery can provide over a 20-hour period that brings the voltage to 10.5 volts with an ambient temperature of 25 degrees Celsius.

Marine Batteries And Car Batteries Are Designed Differently

Marine batteries and car batteries share some common features but have major differences in design. This means that if you need a marine battery, you will get far better results by purchasing a specific marine battery than you will by using a battery designed for a car. Since automotive batteries do not need to discharge energy after starting the car′s engine, they are typically designed with thinner internal plates than a marine battery. The housing of the marine battery is thicker to better insulate the battery from vibration and shock. After all, the amount of vibration in a vessel is much greater than it is in a car. This better insulation will provide a longer lifespan in the marine environment. Marine batteries are designed specifically to meet the needs of power boats; they are stronger, heavier and suited to the unique needs of a power boat.

Purchasing an automotive battery can seem like a great way to save money as they are usually priced lower than a true marine battery, but there is a significant chance that you will end up replacing them more often, they will be less reliable and in the end more costly.

Battery Troubleshooting

My boat smells like battery acid and the batteries are hot to the touch! This is likely caused by overcharging, a defective battery or a defective charger. Modern computer controlled battery chargers use programmed charge profiles for the different types of batteries. There is a specific profile for flooded batteries, a different one for sealed batteries, different still for gel batteries and one different for the AGM battery. If set properly, modern battery chargers will not overcharge the battery and still bring it to 100% of capacity. But if the battery is defective or the recharge voltage too high, the battery will gas and your engine room will smell like acid. Using the correct AC battery charger for the type of battery you are using is critical to getting the best performance and life from our battery investment.

A good voltmeter will reveal a lot about your battery and the charging system. Twelve volt batteries will measure between 12.60 and 12.80 volts when fully charged, at 50% charge they will measure around 12.10 volts and when fully discharged will be around 10.60 volts. Discharge a battery bellow 10.50 volts, and you have probably killed it or at a minimum severely shortened its useful life. Although the recharge voltage for different battery types varies you can expect to see maximum recharge voltages around 14.40 volts. Any higher and the battery will begin to boil, turning the liquid acid into hydrogen and oxygen gas, and causing the battery to vent. Charging with a lower voltage will not bring the battery to full capacity and over time it will lose that capacity due to sulfation. Don′t forget to check the engine alternator also. If the voltage at the battery does not change from 12.60 volts to 14.40 volts when the engine is started, there may be a problem with alternator. If the voltage from the alternator is higher than 14.40 volts something is wrong and needs to be sorted out quickly as the high voltage is negatively impacting the health of your batteries.

Most battery installations have multiple batteries connected in parallel, and in vessels that have 24-volt systems, batteries will be connected in a series/parallel arrangement. In order to troubleshoot and measure the condition of each battery they must be fully charged and be isolated from each other. The best solution to isolate the batteries after they are fully charged is to remove the positive cable from each battery terminal being careful that the now exposed positive terminal does not come in contact with any negative terminal or vessel metal parts. Once isolated a standard test of battery health is to measure the voltage while applying a load to the fully charged battery. If a bad or weak battery is found within a bank of series or parallel-connected batteries, that bad battery will deep discharge the other batteries in the bank. All of the batteries should be replaced not just the one(s) that measure weak.

Lithium Ion Batteries

No article on batteries would be complete without at least a few words on the best battery technology available today, the Lithium Ion battery, or Li-Ion. Li-Ion batteries have a high energy density, offering savings of up to 70% in volume and weight compared to traditional lead acid batteries. They are perfect for cyclic applications, making over 2000 cycles with very deep (80%) discharges, effectively storing five times as much energy over its lifespan compared to lead acid chemistry.

The expected life of the Li-Ion battery is as long as the best of the AGM batteries available, but have added advantages of lighter weight for the same energy capacity, extremely fast recharge times and a high number of deep discharge cycles tolerated. The downsides, and there are a few, can be dangerous. Puncture a Li-Ion battery and allow oxygen to contact the Li, and it will quickly combust. Try to extinguish the resultant fire with water, and you will be feeding the chemical reaction and make the fire more extreme. Recharging must be tightly controlled with a purpose designed charger. There are no low cost options. Overcharge a Li-Ion battery and its failure mode is to heat up. If it gets too hot it will burst into flames.

The term Lithium Ion encompasses multiple chemistries, having slightly different compositions of additive materials. These differences result in variations of energy and power density, lifespan, cost and safety. The most common of the Li-Ion batteries is the Lithium Cobalt Oxide, LiCoO2, which is prevalent in mobile phones and computers where low current drain over longer periods of time is desirable. Another common chemistry is the Lithium Nickel Manganese Cobalt Oxide, LiNiMnCoO2, these batteries are common in applications requiring high currents and fast recharge times such as power tools. Optimized for electric car or traction motor applications is the Lithium Nickel Cobalt Aluminum Oxide, LiNiCoAlO2.

Another chemistry now making its way into the recreational marine market is the Lithium Iron Phosphate, LiFePO4. Key benefits are a high current rating and a long cycle life, good thermal stability, enhanced safety and tolerance if abused. Just what the doctor ordered for marine applications. The only downside to the Lithium Phosphate battery is lower energy density and higher self discharge rate than other Li-Ion chemistries, but these are good tradeoffs in the marine environment for the improvement of safety.

Proper Recharging Is Critical For Best Performance

The lifespan of any battery will vary considerably with how it has been treated, maintained and recharged. If kept in full state of charge when not being used, never discharged below 20% of its capacity and using a modern multi stage charger an AGM battery can be expected to last 8 years or 500 charge/discharge cycles. A new Lithium Phosphate battery has an expected life of 2,000 charge/discharge cycles before needed replacement.

No matter what the chemistry you are using, if you want to shorten the life of your battery investment, do these three things and your expensive batteries will die young.

  1. Use the wrong charge profile. Too low a charge voltage and the battery will not reach 100% of capacity, the plates will sulfate, and capacity will be forever lost. Too high a voltage and the batteries will generate gas, leading to loss of electrolyte and reduced capacity.
  2. Discharging the battery below 20% of capacity. Over discharging a battery or leaving a load on the battery for days, and the lifespan will be severely shortened if not outright killing it.
  3. Using fixed voltage cheap or old fashioned chargers that have high ripple voltages will quickly shorten the batteries life. When looking for a battery charger, do not be tempted to select the cheapest available. There is a reason it is cheap.

Lessons Learned?

Early battery failure is usually caused for three reasons; neglect, abuse, or having the wrong battery for the application. Flooded batteries need regular attention and if neglected for even a few months will cause early failure. The water in each cell must be checked at least monthly and topped up as necessary. Any exposure of the plates to air will cause permanent loss of capacity and will start the failure process. These batteries also need regular cleaning of the terminals due to the gasses emitted when charging.

The sealed batteries can only tolerate some abuse. Overcharging or deep discharging will shorten their life. If you find corrosion around the terminal of a SLA battery then something is wrong with the way you are treating the battery. Overcharging will cause even a sealed battery to vent gasses. Although more costly, the AGM battery eliminates neglect. They don′t require any regular inspection or maintenance, they really are maintenance free.

Using a storage battery in a starting application will shorten the life of the battery. The same is true of using a starting battery in a storage application. Choose the correct battery for the application or at a minimum use a dual purpose battery. Do not simply consider the initial cost of the battery when deciding on which to purchase. If you plan on keeping your boat for a long time, then the added initial expense of the AGM battery makes sense. They cost twice that of the sealed battery, but they can last three times as long. I put a set in my boat when I purchased it 8 years ago. Using a load tester shows them to still have 85% of the capacity still available. Yep, they cost a lot, but I haven′t had to think about batteries.

Get rid of those wing nuts. Here is a photo of a battery that melted the terminal because the wing nut was loose. Current marine best practices do not allow the use of wing nuts on battery terminals because vibration can cause them to loosen. Replace them with a good brass or stainless nut and lock washers.

Remember the more difficult is to get to the battery the less often you are likely to check it. SLA or AGM batteries are very attractive for those of you that do not do maintenance on a regular schedule or do not pay someone to do it for you.

Now it time to kick back and enjoy a good port and cigar while I watch my AGM batteries take care of themselves and contemplate their replacement with Carbon Foam or Li-Ion when the time comes. Until next month please keep those letters coming. Have a good story to tell, send me an email. I love a good story patcarson@yachtsmanmagazine.com H


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