AGM and gel cell batteries are considered maintenance free. They can be installed on their sides if necessary as there is no danger of fluid leaking from the battery. These batteries do not require regular filling with water, they are self-contained. Gel batteries are not used as much anymore and are usually replaced with an AGM style.
Maintenance free does not mean the battery does not need to be inspected and cared for, you will still need to keep it charged in times when the boat is not in use and check terminals and ventilation on a regular basis.
Battery life is determined by the number of cycles it goes through and how good the unit is at withstanding frequent discharges. How much the battery is discharged, percentage-wise, with each use will also impact how long it lasts. Discharging a battery completely down to zero will render it incapable of being recharged and worthless.
Starting Batteries Defined
Starting or cranking batteries have only one job, to start the engine of the boat. They are designed to give off short, high bursts of power. These batteries have a lot of lead plates and they are thinner than they would be in other types of batteries to ensure a quick recharge time. Your boat’s engine specs will dictate how many CCAs (cold cranking amps) you will need. Starting batteries are not useful in putting out deep discharges and will not last very long if that is the case.
Cold cranking amps are the number of amps a battery can put out at 0°F for 30 seconds. If the battery lists MCAs, marine cold cranking amps, this is the same measurement except tested at 32°F.
These batteries are good choices for outboards and smaller vessels.
Deep Cycle Batteries Defined
Deep cycle batteries are made to handle the electrical load of the accessories on your vessel. Lights, fish finders, radios, etc. are all powered by the deep cycle. This battery type is characterized by thick lead plates that are optimum for storing or banking power for later use. The deep cycle will run accessories on its own power even if not being charged by the alternator or another power source. Cruiser vessels will require one or more powerful batteries like this to provide for the electrical equipment on board.
The battery is rechargeable and once discharged and power is full again, it is ready to go once more.
Dual Purpose Batteries Defined
The dual purpose battery is just what it sounds like – it is capable of handling both starting duties and powering accessories. The dual purpose does not have as much storing capacity as the deep cycle, however, so this may be a factor for you when deciding which type of battery works for you. These are a good option if you do not discharge your battery below 50%. If you do tend to do that regularly, then a deep cycle is the better choice. A dual purpose would be good for sailboats with identical interchangeable batteries.
Which One Do You Need?
When determining which battery is the best fit for your boat, look at the variety of issues mentioned in the above paragraphs. Check your manufacturer’s specs to be certain you choose a battery that meets at least the minimum requirements. Cold cranking amp ratings are going to be a factor for your starter battery. The amount of room you have to install the battery will limit how big a battery you can fit in the battery compartment. Do a run through of all the accessories on the boat, and if you have a lot of electrical options and add-ons, then be sure to purchase a battery with enough storage capacity to run all those electrical gadgets.
One thing to check for is the rating of the deep cycle batteries. You will see 20hr capacity ratings noted on the battery. This is a standard unit of measurement for battery storage capacity. All deep cycles are noted with this and it indicates how long it took to fully discharge the battery over a 20 hour period. This ensures that a universal measurement system is being used so that when you are considering batteries, you are comparing “apples to apples”, so to speak. (ex. A rating of 100AH @ 20HR means the battery is totally discharged in 20 hours running a 5 amp load.)
PURCHASING AND INSTALLATION TIPS
While looking for a new battery, do not fall into the temptation to purchase an automotive battery for your boat. Though they may look similar, the internal design and components of these batteries are very different and using a car battery is bound to leave you stranded pretty quickly.
Installation is important. You want to protect your investment. Make sure you have a sturdy plastic box for mounting the battery to protect it. The battery needs to be well ventilated to prevent the build-up of gasses. Nothing should be laid on top of the battery and connections should be secure and checked frequently. Be careful and do not assume that all sealed batteries can be laid on their sides for mounting, some still have a danger of leaking. Check with each manufacturer regarding the mounting capabilities of your battery.