The key to helping your batteries to last longer and perform at their best is to keep them fully charged. A healthy battery is a fully charged battery. It is essential to watch the depth of discharge (DoD), a critical factor in its life and performance. Left at a deep discharge level, a battery will have a short life and struggle to maintain its charge. Lead Sulphate crystals will build up within a discharged battery, and over time, will prevent it from fully charging and eventually fail altogether. This is the most common cause of battery failure, so keeping them fully charged and healthy is sensible.

It all starts with battery choice

A starter battery such as the VETUS VESMF (SMF = Sealed Maintenance Free) has been developed to provide a lot of energy almost instantly, sufficient to power up the engine at the turn of the key. But this type of (cranking power) battery has been designed for that specific purpose, which it does very well, but it is not suitable to run the boat’s domestic and navigation systems. A battery like this can be damaged by taking lower loads over more extended periods. If the SMF battery is discharged too deep, it will almost certainly struggle to regain capacity in the future and fail after a couple of seasons if used in this way. A VESMF battery will provide a reliable and robust energy source to start the engine, but the boat will also need a dedicated system battery to run other equipment.

The VEAGM (AGM = Absorbed Glass Mat) is a more suitable battery for both large and smaller endurance service loads. The VEAGM batteries have both starter and deep-cycle marine battery characteristics (also known as a dual purpose battery). This battery will last many seasons if well cared for, and if your boat has only one battery, it is the best option.

The traditional VEDC110TC is a cost-effective deep-cycle lead acid battery, one size only of 110 ah and providing a great deal of battery power for the price.

It is worth taking care in selecting the correct battery for the job, as the wrong choice may seriously reduce the battery’s life. A starter battery could be fitted on a fishing or leisure boat needing just one battery. Still, if it is used beyond the engine starting, it will be unable to handle the slower and lower load pull of other electrical equipment and could quickly lose capacity and fail. The more versatile VEAGM or the conventional VEDC110 would be the practical choice.

How long can I expect my batteries to last?

The depth of discharge (DoD) is the main factor here. The DoD refers to the amount of energy that has been discharged from a battery compared to its total capacity. In a marine battery’s case, the discharge depth indicates how much of the battery’s capacity has been utilized during a particular usage cycle.

Batteries should not be left partially or deeply discharged for more than a few hours. When you take 100% of the power out of a marine battery and recharge immediately, it is considered as one cycle. This can only be achieved 10-15 times before capacity drops. If the battery has been discharged 75% before fully recharging, it can achieve 500-600 cycles, equivalent to an average boat owner’s 6-7 years of boating. Less than 75% of discharge and cycles can reach the thousands. Proper battery charging and maintenance practices, such as avoiding excessive deep discharges and regularly recharging the battery, can help ensure its longevity and reliability.

Typically, long-distance sailing cruisers suffer the most from battery DoD as the engine is not used sufficiently to charge the battery up to 100%. Charging can be short-lived, and the battery will slowly deteriorate. Therefore, sailboats often need to change their batteries more frequently.

How do I keep my marine batteries fully charged?

The two main methods of battery charging are via engine usage through the alternator and with shore power connected to an onboard charger. However, always ensure you have a good-quality charger. Simple chargers can either overcharge, causing battery damage or undercharge and not fully charge the battery, which will then start to lose its capacity.

Charging a discharged battery back up to 100% is done in 3 phases. If the battery is down to a 25% state of charge, the first bulk phase is fast, quickly getting the battery up to 80% in a couple of hours, but then the voltage builds, and the charging will slow to avoid the voltage getting too high. From 80% to 95%, the absorption phase takes longer to avoid “gassing,” which occurs when the voltage gets too high. The last float phase to 100% can take 10-12 hours, which is critical to ensure a healthy battery. A quality charger will take the battery through all these phases in a controlled manner.

Be smart with your battery care.

Most owners with regular use will get 4/5 years from their battery, but a smart owner can earn more by applying a few simple rules to battery maintenance. Installation of a battery monitor can help to tell the owner when capacity is getting low, and it is time to start the engine or head for the shore power. A voltmeter is not accurate enough to do the job and can only be regarded as an indicator, so a battery monitor is a great investment.

Installing a battery main switch will prevent power loss through minor services and stand-by indicators being left on after leaving the boat. Fitting a 2nd alternator (if the battery size allows this) will also speed up charging when the engines are in use.

If a high-power charger is used, it is worth fitting a temperature gauge to ensure the temperature does not rise too high during charging. Keeping the battery cool can give an extra season’s happy boating. When fitting the new marine batteries, keep them isolated as much as possible from the heat of the engines. Place a rubber mat under the batteries to avoid vibration and ensure the cables are identical to ensure each battery receives the same charge level.

Do not mix different types of battery in a battery bank. If one battery starts to fail, change them all as it is best to keep all batteries of the same type, age, and capacity. A failing battery will always influence the others in the battery bank. These simple steps can add at least another year of life to your marine batteries.

Arthur Roeling, Director R&D and Service at VETUS said: “The batteries are the beating heart of a boat, providing the ability to start the engine, drop the anchor, run the chart plotter, the fridge and all the important systems essential to the safe running of a modern vessel. So don’t wait to charge the batteries until the lights go dim, it makes sense to maintain and keep the batteries fully charged. Here at VETUS we have developed high-quality, long-lasting batteries and battery management systems to keep your boat safe and running for many years of trouble-free boating. So, look after your marine batteries and they will look after you.”

Click here to check out our video blog about battery maintenance.

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