Batteries are the heart of your boats electrical system. They can also be a very dangerous part of your electrical system if not correctly installed. Batteries contain a large amount of energy along with some not pleasant chemicals, which can leak causing corrosion and damage to your boats structure. Poor ventilation of installed batteries can cause excessive gassing, overheating which could lead to an explosion. Given these potential problems it is important to make sure your batteries are properly installed to remain safe.
As a marine surveyor I get to see a lot of battery installations some better than others. Based on what I have seen, it is clear many owners do not fully understand what makes for a safe installation. Properly installed batteries are not only safer but will last longer saving money in the long run. A poorly installed battery system on the other hand can become a hazard and may not provide the dependable power needed. Many owners and even some boat builders do a poor job of properly installing batteries so that they will provide safe dependable power.
Fortunately there is a set of guidelines that can help insure the batteries are properly installed to avoid problems. The American Boat and Yacht Council (ABYC) has developed a set of common sense recommendations on how to install batteries to ensure they remain safe and will provide the power needed when it is needed. Now I know many get defensive when they hear talk about meeting “rules and regulations” and I get that, but I think most will agree these rules make sense. Before you lose interest thinking I am going to recite a bunch of regulations, fear not, I am just going to focus on the how and whys of a good battery installation. In the end your installation will be in “code” if you follow these recommendations.
The common marine batteries are the lead acid wet cell type commonly associated with car batteries. They are heavy and filled with an acid solution referred to as electrolyte, a solution of roughly 70% water and 30% sulfuric acid. Most are vented on the top to allow hydrogen and oxygen gases to escape during charging. Yep they produce Hydrogen gas, a highly explosive gas and corrosive gas, the same stuff that brought down the Hindenburg Zeppelin. These gases are what cause batteries to explode when things go wrong. Many boaters will also use gel cell or AGM batteries and although many of these are sealed they can and do release gases when over charged and these batteries have also been known to explode.
Regardless of the battery type the installations should be the same. Batteries work by a chemical reaction and these chemicals can be a hazard if spilled. Batteries also contain a large amount of electrical energy. The bigger the battery or battery bank the greater the energy potential they will have. Anyone who has ever accidently shorted a battery knows only too well the power of that energy. It can easily melt metal as well as start fires. It goes without saying that keeping this energy and the acidic chemicals properly under control is important. Add to that the weight of the batteries and the movement of the boat and it becomes clear how important a good installation is.
Any battery installation needs to meet a few basic requirements to not only be safe but to help protect and secure the batteries from damage. It also needs to be kept in mind that no matter what type of battery being used the requirements will be the same. With modern sealed batteries some will argue that these batteries do not leak and therefore do not need boxes. The truth is all batteries can fail sometimes catastrophically and it is important to protect the boat and equipment from subsequent damage. It also needs to be kept in mind that replacement batteries may not be the same as the being replaced. A proper installation will be safe for all types of batteries likely to be used.
To start with think about how the batteries are mounted in the boat. The first consideration is where to install the batteries. This is often already decided by the boats builder but if adding batteries or installing larger batteries some changes may need to be made. Many builders install batteries almost as if they were an after thought so it might pay to review the builder’s installation to see if improvements can be made as well, do not assume the builder got it right not all do.
When picking a location for the batteries there are a few things to keep in mind. As batteries are heavy the weight should be down low in the boat. You also want easy access for maintenance and service. The location should be well vented to eliminate explosive gases and to help cool the batteries. Some space should be provided between the batteries if possible to allow for cooling as well. Batteries packed tightly together cannot properly shed excess heat. Batteries are less efficient and their life will be shorter if they are constantly hot. You also do not want anything directly over the batteries this is particularly true with battery chargers, inverters, and other electronic equipment. This is not only to prevent explosion hazards but to protect the equipment from corrosive gases. Hydrogen and oxygen gases are corrosive and will shorten the life of electrical equipment mounted above or too close to a battery. The most common location for batteries is in the engine compartment. Batteries in the engine compartment may seem to be in conflict with the heat requirement but if they have good air flow this will not be a real problem.
Once a suitable location has been worked out the way the batteries are mounted to the boat needs to be considered. A box or tray preferably with a lid should be used to contain any leaking fluids. Should a battery fail catastrophically a box with a lid will help contain the carnage. A good box and lid will also help protect the batteries form damage from an outside source such as stowed equipment. It is acceptable to use a single box for more than one battery but if doing this leave a bit of separation between the batteries to reduce heat buildup when charging. I often get the argument that a box or tray is not needed with sealed batteries. ABYC uses the logic that at some point the sealed battery may be replaced with a wet cell which is a valid argument. Sealed batteries can and do explode although it is not as common. Finally the box does help protect the battery from outside damage as mentioned. All good reasons to have the batteries in a box.
It is also important to make sure the battery is well secured to the boat. ABYC recommends that the battery be secured so as to not move more than one inch in any direction with a force equal to the weight of the battery. This is really common sense and even more important for boats that may venture offshore. Most of the battery tie down straps found in local marine supply stores do not come close to being strong enough to secure the average battery. Even some of the better tie down straps only use small screws to secure the strap to the boat. A better system is to use ratchet type cargo straps connected to eye bolts secured to the vessel. Cross bars with threaded rods bolted to the boat also work well. Make sure the tie downs do not block any vents on the battery, the vents may not be obvious on sealed batteries but they will be there. Try to imagine that you turned the boat upside down and shook it. Would the battery remain in place? This may seem extreme but it is a worst case scenario and it is not that hard to properly secure the batteries for even this extreme case. I have heard of batteries coming loose in less severe conditions and the results are never good. Keep in mind it is the sever condition that the batteries will likely be needed most.
Any battery installation will require some ventilation. This does not necessarily need to be a forced air system using a blower but could be natural ventilation if the air flow is reasonable as in an engine compartment. For batteries stuck under a bunk or in any area without air flow it is wise to add some ventilation. You want to do this primarily to remove flammable and corrosive gases and secondly to help cool the batteries particularly during charging cycles. I have seen some installations using a small computer fan on a voltage sensing switch. When the voltage increases due to charging the fan comes on. Charging is when the most heat and gasses will be produced and when ventilation is needed most.
Batteries contain a lot of electrical energy, hundreds of amps in most installations. This energy is always ready and willing to be released. Because of this ABYC recommends covering the positive terminals on batteries to prevent accidental shorting. If you have ever accidently shorted a battery you will understand the reasoning on this. A battery in a box with a lid will meet this requirement but if that is not possible there are several companies that make rubber boots to cover the positive terminals. In a pinch split hoses will work the idea is to protect the positive post and connections from accidental contact with anything that could short it out.
The batteries should also be located where they will be accessible for inspection and service. This is particularly true for wet cell batteries but it is also important for sealed batteries. With wet cell batteries it is of course important to be able to check the fluid level but all batteries should be inspected for physical problems as well. It is important to check all the wire connections as well as the general condition of the battery. Swelling cases and or cracks can be a sign of problems. It is also a good idea to check the battery temperature with an IR thermometer, a hot battery is a sign of a possible failing battery.
With the batteries properly mounted the last part of the installation is connecting the wires. This is another area where problems and poor installation occur. It is common to see several wires all piled onto a single post and in some cases some creative engineering to increase the number of wires on that can fit on to a single post. ABYC recommendations only allow four connections to a single stud. This makes sense as the more conductors on a stud the more likely you will end up with poor connections. When it comes to making connections to the battery post, less is better. The best arrangement is to have only one cable connected to each post securely fastened with a clamp or nut. Wing nuts should not be used as they are harder to get tight and not approved by ABYC. The connection should be checked regularly for tightness and any corrosion.
The single cables from the battery should go directly to a battery switch on the positive side and a buss bar on the negative side. It is best to keep the battery switch as close to the battery as practical while still remaining easy to access in an emergency. Several companies such as Blue Seas now make remote battery switches making it even easier to have the switch close to the battery.
After the battery switch should be a sub panel with breakers or fuses for all those wires that would have been connected directly to the battery. Any Starter cables can go directly from the switch to the starter without a fuse or breaker. Many boat builders are now installing sub panels like this near the batteries. These subpanels will have breakers for equipment such as automatic bilge pumps, alarms, monitors, stereo memories, and anything that should not be turned off by accident. This setup works well for safety and reducing clutter at the battery. All ground wires should go to a buss bar located at or near the sub panel.
A good battery installation is not hard to achieve it just takes a bit of effort and some common sense. A proper installation will not only help keep your boat safe but will also increase the life of your batteries. It will also help protect the boat from damage due to acids and corrosive gases. It may pay to review your installation and try to incorporate as much of these “rules” as you can. There are several great products from battery boxes to buss bars that will help make a proper installation easier. Remember a poorly installed battery is a hazard to both the crew and the vessel, it will likely also shorten the life of the battery.
By Capt. Wayne Canning, AMS
If you found this helpful please return the favor to keep the information (and rum) flowing. Please consider helping out with a bit cash. I am a cheap ass sailor and every little bit helps! Thanks!
If you are thinking of buying a product related to the article please check the Amazon link below. I never refer any product I would not buy or have bought myself.
You are right on track when you mention to check installation of batteries in a brand new boat. My Rosborough installed batteries with the wrong battery charger and still do. If any draw from a pump light, the charger would go through maintenance mode and over charge (boil the batteries.) Seeing they are mounted under a hatch in the cabin, they filled the space with hydrogen setting off the CO detectors. I have notified the builder of this very dangerous set up to no avail. The builder is Eastern Boats in New Hampshire. I replaced all batteries with AGM and replaced with the proper charger and fan at at my own expense. This builder should be investigated.