Boat Battery Essential Buying Guide

A battery is an energy reservoir, and the majority of marine batteries are of the lead-acid format. The battery provides power when acid in the electrolyte solution begins the combine with the lead in the plates. The acid is subsequently transferred to the plates and the battery discharges it's power. The recharging process forces the acid out of the plates, allowing it to mix with the electrolyte solution once more.

Batteries, although looking pretty simple, are actually quite a complex topic. As a boat owner, it is vitally important that you have a fundamental understanding of boat battery basics. Knowing how a battery works (or doesn't work) is something we'll take a brief look at here, there is plenty of detailed information available online, I urge you to find it. I will be providing some detailed articles on this site at a later date. When we talk about marine battery application, it means the battery use in the type of boat or trolling motor you have. construction is simple, it involves how the battery is constructed.

Types Of Batteries

Many people do not realize that, for marine craft, there are actually a couple of types of battery, designed for different purposes.. These are:

Marine Cranking Batteries

Also known as a starting battery, and as the name implies, they are used to provide efficient starting of the main engines on your boat. An engine needs a lot of power to turn over, and the cranking battery is specifically designed to meet this need. The cranking battery is designed with a large number of thin plates which exposes a much larger plate area to the electrolyte solution. This allows for the utilization of a lot of power to turn the engine over. The boats battery charging system will replenish the battery quickly when the engines are running. A poorly maintained boat battery will let you down, but so will a neglected charging system.

What Is The Marine Cranking Amp (MCA)

One of the most important things you need to know when buying a new boat battery, is the concept of the marine cranking amp. You will find this figure displayed on the batteries label. This number, as shown on the right, will tell you how good this battery is at starting an engine. Before heading out and buying a new marine battery, take a look in your engines manual to check the MCA you need. Alternatively, a visit to the engine manufacturers website  or a local engine dealer may provide you with the information you need.

If you can afford to get a battery with a higher MCA rating, this is a good buffer against a bad day when the engine starting is giving you problems. It's nice to have that extra margin of safety!

Boat Battery Design

The humble marine battery is the central item in the electrical system of all pleasure craft. Most boats have a simple 12 volt DC system. The marine battery is usually set in banks of one, two, three, or four industrial batteries which hare connected in parallel. A larger vessel may have a 24 or 36 volt marine battery system. In general, each battery is utilized to start one engine, but it is also wired to a battery selector switch.

This switch may be marked 1, 2 ,or ALL. The selector switch controls which battery bank runs the house system. Modern yachting codes state that all boats must have a master shut off switch for safety reasons.

The use of boat battery parallel switches join two batteries together which results in a doubling of amperage but not a doubling in voltage. If both batteries are low they may start an engine that fails to start on a single bank but this is not always the case, hence the need to ensure that marine batteries are well charged and in good condition.

Marine Battery Types

There are a number of types of replacement lead acid sealed batteries, and they are not all created equally. Automotive or Starting batteries, Both marine cycle batteries and deep cycle batteries are very different creatures. Real deep cycle batteries have extremely thick plates, and are much heavier duty than the hybrid pseudo deep cycle batteries that are often found on sale or for use as golf cart batteries. In fact, the thickness and composition of the battery plates are the major contributor to cost.

Cycling is the period of discharging and recharging the battery, and the life of a battery is determined by how many times the cycle takes place. An automotive battery is designed to withstand 5% discharges, whereas a deep cycle unit can withstand 50% discharges without sustaining damage.

The starting or automotive battery is often found in entry level boats and are touted as marine batteries (sometimes called auto/marine). The problem here is that an automotive battery is designed to be constantly trickle charged by your alternator, thus avoiding discharge rates or greater than the safe 5%. The sort of batteries marine vessels should use is likely to be a deep cycle battery, although hybrids are common.

The Deep Cycle Boat Battery

The plates will be thicker than the automotive types but not as thick as a true boat battery. As mentioned, marine deep cycle batteries can tolerate 50% discharge, your industrial deep cyclers can take an 80% discharge without permanent damage. An automotive battery will suffer irreparable damage at these rates. So just because the boat battery you have is labeled auto/marine, don't assume that it is going to do a great job. There is really no way of telling unless you cut it in half. These types of batteries are well suited for trolling.

Trolling Motor Batteries

The trolling motor uses a lot of power, and over long periods of time. They do not however, need that massive power surge that the marine starting battery does. Trolling motor batteries discharge much more slowly and this is why deep cycle batteries, with much thicker plates, are an ideal boat battery for this type of use.

Another important figure to consider is the reserve capacity (RC). Again, find this on the label on your battery, and this number will indicate how long the battery can carry the specified load before it fails. Look for a trolling battery with a high RC for longer duration trolling.

Dual Purpose Marine Batteries

There is no doubt that the ideal, and optimum strategy for installing boat batteries is to have a cranking battery for engine starting, and a deep cycle battery for trolling and running ancillary electrical equipment. Due to the use of smaller vessels, there is an alternative available. The dual purpose battery is ideal for smaller boats with a 12 volt trolling motor and a single battery electrical system installed.

As you can imagine, this battery is not as good at starting an engine as a single purpose cranking battery, nor as effective for trolling as a deep cycle battery, but it will perform both tasks to a good level, providing you make sure that it is up to the job for YOUR vessel. The preferred option is to install a dual battery system, but for many smaller vessel owners, the dual purpose battery is a viable compromise.

One of the major causes of failure of marine batteries is the incorrect type being used, the wrong size, or a poor quality boat battery being fitted. One needs to fit the right size boat battery to fit the crafts requirements, anything less might work for a short period of time but is likely to let you down just when you need it most. A good quality marine battery is not cheap, and a lot of boats are sold with the lowest quality battery the retailer can get away with. This is not always the case, but always check the quality of the boat battery when buying a vessel, and ask for an upgrade if you are not happy.

For quality products,  Amazon  are hard to beat. They offer a great range of boat batteries  from reputable manufacturers like Duralast , Optima and MRG. as well as accessories like the boat battery charger and selector switches.

The use of the electronic boat battery charger, now the prevalent type these days virtually eliminate the risk of overcharging. They provide a 3 stage charging routine and use electronic sensors to monitor the charging process and prevent the boat battery being overcharged. An old electric charger may well be the cause of damage to your marine cycle battery if you are experiencing power problems. Unusual fluid loss and a hotter than usual battery rate likely signs of overcharging.

On this basis, it is important that you check the marine battery you have in your vessel and try to determine the quality of it. If in doubt replace it with a bespoke boating battery which should provide you with good, reliable service providing you give it the correct maintenance. Taking a chance with a boat battery is a bad idea, and many a sailor has come undone on the water by trusting a defective boat battery.

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