The Humble and Hard-Working Boat Battery Box

There seems to be a lot of confusion and misconception out there regarding the humble boat battery box. There are those who believe they are bad for batteries and others who think they're the greatest thing since the ship's wheel. Some insist the law states that boat batteries need to be in a box, others will say that that keeping them in a boat battery box is not required by law. Read on and get un-confused.

Do Boat Batteries Need to Be In a Box?

Most boats have at least one battery, no matter their size. Even a diminutive dinghy might have a battery onboard because of the navigation electronics or lights. While onboard electricity is a fantastic thing to have, it comes at the expense of boat real estate, and not just any real estate--the battery must be put in a safe place out of the way where it won't be tripped over, have something fall on it, or worse, become an object of interest to a curious child.

The Coast Guard does not require that boat batteries be in boxes, but they do require that they are at least securely strapped down to prevent movement and the posts covered to prevent accidental contact with the terminals. The marine section of the code of federal regulations has a section specifically on batteries and these should be followed as it makes having a battery onboard not only in compliance but also much safer for you and your passengers.

Originally all batteries were of the wet lead acid type. The corrosive acid would either leak or vaporize out, creating potentially destructive issues. One way to reduce this was to place the batteries in a non-corrosive enclosure. Nowadays we have more of a selection of batteries, but even the so-called maintenance-free sealed batteries give off gas and emit corrosive vapor, and this is one of many reasons why a lot of boaters refuse to store their batteries anywhere other than a boat battery box.

This is also one reason many other boaters refuse to use battery boxes! They are under the impression that the gasses emitted by the batteries will become trapped in the battery box and cause an explosion. This would be a valid concern, except that battery boxes have ventilation to prevent just such a frightening scenario. While there is no official Coast Guard Approved battery box, there are boxes that comply with USCG code regulation #33 which have plenty of ventilation, such as this one by Todd USA, who makes more than just boat seats!

Lithium-ion Batteries 

Lithium-ion batteries, also called Li-ion, don't need a battery box because they do not contain corrosive acid and do not off-gas, but they must still be securely housed to prevent any movement and the terminals must be covered. This may sound like the easier (albeit extremely expensive) way to go, but Li-ion technology is still in its early stages as the rash of exploding Li-ion batteries shows, and installing them in your boat could be risky business. Sometimes Li-ions get overcharged and then get hot, and what's worse, some of them continue to get hotter even if taken off the charge--these have suddenly taken a flying leap into a nasty process called thermal runaway.

Thermal runaway is when a battery's cell--and it only takes one--gets hot enough to jump into thermal runaway, another cell next to it overheats, and it in turn will overheat the next one, and so on. This results in an ugly cascade effect as the battery catches fire and burns uncontrollably. Li-ions come in many different chemical makeups; for example, some manufacturers combine the lithium in their batteries with manganese oxide, others with nickel manganese cobalt, or iron phosphate, and so on. Some chemicals are more prone to thermal runaway than others.

Nevertheless, some boaters insist on Li-ion batteries. If you're considering this, at the very least get professional advice and installation. This is because Li-ions charge at different voltages than lead-acid batteries do, and can't be connected to a conventional charger. Li-ions need a system that tracks and balances the voltage differences between each cell and has over-voltage and short-circuit protection.

This all may sound quite sophisticated and safe, but get a power surge or lightning strike and it may well be toast. Which of course can mean fire. Professional design and installation of Li-ion battery systems can go a long way toward making them safer. For a quick, interesting read on the safety concerns surrounding the Li-ions of the USCG, take a look at this policy letter from October 2020 written by the Commandant of the USCG. Keep in mind, this was a guidance letter only, nothing that was adding to already existing laws.

Types of Battery Boxes

Commercial-grade battery boxes come in various sizes and shapes to accommodate most batteries and configurations such as a 4D battery box, an 8D battery box, or a dual 6V battery box that houses two six-volt batteries such as those manufactured by Noco Marine.

We have a great selection of battery boxes in many sizes, shapes, and price ranges, plus the installation hardware you'll need such as hold-down kits and battery box straps like this heavy-duty one from Sea-Dog.  If at all possible, it's a good idea always to have a spare battery so as not to be stranded should one give up the ghost. We have a wide range of battery selector switches and on their page, you'll also find a short article about them and how to choose the right one.

All of this won't do you much good without a charger but never fear, we also have plenty of different boat battery chargers to choose from as well.

Using a battery box makes a lot of practical sense because it not only makes for a neater installation but has safety advantages as well. A good battery box will vent any gasses and, if something goes wrong and the battery leaks, will contain the acid and protect the surrounding area from damage. But as mentioned earlier, not every boater is a fan of the humble battery box. We have you covered as well, as we have quite a few different battery trays, so take a look! Whether battery boxes or trays, accessories, or installation necessities, you'll find it here.