April 8

Understanding Marine Electrics: Maximizing Battery Life on Your Boat

In this blogpost, we’ll address a common question: why do boat batteries rarely live up to their published life expectancy, especially when it comes to lead acid batteries? Let's dive in and explore the challenges and how to optimize battery life on your boat.

Published Battery Life Expectancy

For most lead acid batteries you can find published statistics that are generated in a laboratory setting. In these controlled conditions, the battery is discharged to a specific level, usually by 80% of its capacity, and then fully recharged in a controlled ambient temperature. The number of cycles the battery can go through before it fails, which is defined as having its capacity reduced to 80% of its original capacity, is used as a measure of its life expectancy. Unfortunately, the reality of operating a battery on a boat is quite different to laboratory conditions!

Operating Conditions on a Boat

Boat batteries face a unique set of challenges. The temperature on a boat can vary widely, especially if the batteries are installed in an engine room where the ambient temperature can at times be high. This high temperature environment will reduce a battery’s overall lifespan. And then boat batteries frequently are not fully recharged after each discharge cycle, which can lead to a phenomenon called sulfation. This progressively reduces a battery’s capacity.

Replicating Laboratory Conditions on Your Boat for Optimal Battery Life

To optimize battery life on a boat, it is important to create operating conditions that replicate laboratory conditions as closely as possible. This includes managing the temperature of the battery environment and ensuring that the batteries are regularly fully recharged. This often requires ‘smart’ chargers and multi-step voltage regulators, together with establishing a charging regime that is specifically designed for your boat.

Solar Power on an Offshore Boat

A key benefit of solar panels on a boat that is away from dockside power is it helps to maintain the batteries in a higher average state of charge. In general, the higher the average state of charge, the longer the life expectancy. When the boat is not in use, solar power will ensure the batteries remain charged, preventing sulfation.

When the boat is being used, solar power in conjunction with an alternator can help achieve a 100% state of charge on a regular basis. For example, during the summer in the Mediterranean, it's possible to charge with an alternator in the morning and then have solar panels top up the batteries during the day, resulting in batteries that hardly ever go below 70% state of charge and frequently reach 100% state of charge. This is particularly beneficial for those with energy-intensive lifestyles on board, such as running a fridge, freezer, and hot water system.

Importance of Properly Sizing Batteries and Setting Up Charging Regime

With the average cost of a battery bank being several hundred dollars up to thousands of dollars, it is important to ensure that you are getting the most out of your investment. This requires properly sizing the batteries and establishing a charging regime that matches the energy needs of your boat. This will be unique to the way you use your boat and your particular onboard lifestyle. In our Boat Electrics 101 course, we teach you how to properly size, manage and care for your batteries to maximize their lifespan, ultimately saving money in the long run.

If you're looking for more content on this topic, you should definitely check out Nigel's talk on Advances in Batteries & Solar!

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