boat batteries


Many of us take our boat batteries for granted because we are so used to car batteries. However, the reality could not be any more different. Car batteries and boat batteries are very different beasts. Boat batteries require a whole lot more maintenance and care. Here is a Quick Guide to Boat Batteries. This Quick Guide is designed to help you better understand boat batteries, how to look after them and make the right decision the next time you go to buy a boat battery.


There are two types of 12-volt boat batteries. These batteries cannot be substituted for each other. The strengths of one type of battery are the weaknesses of the other. That being said, there are dual cycle batteries that cover both types of jobs to some degree.


Cranking batteries, also known as starting batteries, are specifically designed to start main engines. Cranking batteries recharge much faster than other batteries and they can deliver huge amounts of power for shorter tough jobs. Cranking batteries cannot withstand hundreds of cycles of recharging and discharging.


Deep cycle batteries are built to power on-board accessories and whatever else your boat needs power for. Deep cycle batteries use energy at a much slower rate and don’t normally need to be charged for a full day. Deep cycle batteries can normally handle hundreds of cycles of recharging and discharging.


Boat batteries can also be categorised into 4 other types of batteries.


Wet-cell batteries are the most popularly used batteries. They have a mixture of distilled water and sulfuric acid. They cost less, can be recharged and discharged many times and generally won’t be damaged if you overcharge them. Wet-cell batteries require ventilation because they release hydrogen gas and have the potential to leak corrosive fluid. They also need topping up.


Absorbed Glass Mat batteries have a fibreglass matting that is saturated with an acid (electrolyte) which is squeezed between the plates of the battery. They don’t need refilling, are vibration and shock resistant and have a low self-discharge rate. They are more expensive, heavier and care must be taken with charging currents.


Gel batteries are much like wet-cell batteries because they also have a liquid electrolyte. The electrolyte uses gelled silicates before being sealed. Gel batteries don’t require topping up with water, they are practically maintenance free, can handle low temperatures, vibration and shock resistant and have a very long lifecycle. Unfortunately, they are easily damaged by overcharging, require special chargers and develop a short life span when not regularly charged. They are also cost around double the price of wet-cell batteries.


Lithium-ion batteries are considered super batteries. They are perfect for deep cycle use because of their high energy density. Lithium batteries are around 70% smaller for the same output as a wet-cell battery and can stand many more charging cycles than most other types of batteries. Lithium-ion batteries can handle huge amounts of current allowing for faster recharging. They are often used on high-performance racing boats. Obviously, lithium-ion batteries have a premium price.


Undercharging leads to sulfation, which causes the battery not to work. Overcharging leads to increased corrosion destroying the battery.


Gelled acid and AGM types are essentially maintenance free because they are sealed. Because of this, they need smart technology charging. The most important thing for wet-cell batteries variety is to keep them full. They should be topped off with distilled water as much as possible. Keep connections clean and tight. Petroleum jelly is perfect for protecting connections.

Batteries are best kept out of the cold and will last longer if you disconnect them and bring them out of the weather when not using them. Also, cover the terminals to prevent excess discharging. Don’t use old batteries with new boat batteries as the older batteries will drag the new batteries down.

Always store boat batteries in a cool, dry place.


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Martin White

Martin is huge on everything outdoors and is even bigger on driving and technology. He loves boats, new stuff and writing about it.