The ultimate guide to boat batteries

What you need to know about boat batteries

What is a marine battery?  

Marine batteries are batteries specifically designed for boats. Just like cars, powered boats need batteries along with fuel to move. They have a very robust design that allows them to withstand the high vibrations they’ll experience in any battery-powered boat.

What is a starting battery versus a deep cycle battery?

Your boat typically requires a battery for starting the engine and (if required) powering electronic devices. There are three common types of batteries used in boats: starting batteries, deep cycle batteries, and dual-purpose batteries.

Depending on your specific requirements, your boat may need a starting battery, or it may require both a starting battery and a deep cycle or dual-purpose battery. It's important to assess your power needs and usage patterns to determine the best battery setup for your boat.

Starting batteries provide a quick, powerful jolt of amperes (energy) to start a marine engine. They are built to quickly recharge by the engine alternator. They are not designed to provide energy over a long period of time, so should not be used to power trolling motors or onboard appliances.

Deep cycle batteries run the electronic equipment on a boat, such as radios, DC lights, trolling motors, sounders and other accessories. They are not designed for starting engines. Deep cycle batteries provide less cranking power and recharge more slowly but can operate for longer, discharging deeply and slowly over a long period of time.

There are also dual-purpose batteries that provide both starting and deep cycle use. They aren’t as efficient as using separate batteries but can be convenient on smaller vessels with no room for two batteries. They usually have a shorter lifespan, as they need to provide energy for all purposes on your boat.

What is the best type of marine battery?

There are four common models of marine batteries:

• Flooded lead-acid batteries, e.g. wet-cell batteries
  
• Gel batteries
  
• Lithium-ion batteries
  
• Absorbent glass mat (AGM) batteries.
  

Lithium batteries are the premium marine battery choice. They don't require maintenance, have a longer service life, and are superior in their deep cycle ability. They are much more expensive than other batteries, however, so if your budget is restricted then the next-best alternative is an AGM battery.

AGM batteries are premium lead-acid batteries. They have an extremely high vibration resistance to handle tough marine environments. They can also withstand cycling (discharging and recharging) far better than a flooded battery. Finally, they won’t leak battery acid even if the case is cracked or damaged, so they can be mounted in any orientation. While AGM batteries have a higher initial cost than other lead-acid batteries, they have a longer service life if maintained correctly.

Can I use a car battery in my boat?

You should never use a car battery in your boat rather than a marine battery. Car batteries cannot deal with the harsh vibrations experienced in marine environments. They also cannot provide the same level of deep cycling ability as you would get with a marine deep cycle or dual-purpose battery.

How long do marine batteries last?

Boat batteries last an average of three to four years, although they can last up to six years, depending on the type and usage conditions. Keep your batteries away from excessive heat and connected to a maintenance charger when not in use to help maximise their lifespan. Make sure to regularly test your battery before use to ensure you don’t end up on the water with a flat battery.

Can you overcharge or undercharge a marine battery?

Marine batteries need to be properly charged to last. Always use a charger that meets your boat battery manufacturer’s recommendations.

For lead acid batteries, regularly undercharging your boat battery will lead to ‘sulfation’: sulphate crystals forming on the plates, reducing the battery’s ability to charge and negatively impacting battery performance.

Excessive overcharging is also damaging to boat batteries (especially AGM and gel batteries), ‘cooking’ the battery and leading to corrosion and faster discharges. Make sure to follow the manufacturer's charging recommendations to avoid overcharging.

The best way to preserve your marine battery’s charge is to invest in a multistage charger like SmartCharge.

How do I maintain my marine battery?

Marine batteries need to be kept clean, charged and topped up with water, if required.

Batteries that aren’t kept charged can freeze in cold temperatures and experience cracked cases. Use a maintenance charger like SmartCharge to keep it charged when not in use.

Regularly inspect your battery’s external components, checking that the lead posts don’t show signs of coming off and that there are no signs of corrosion on exposed metal terminals. At least once a year, you should clean out the battery box, check for signs of leaks, inspect the tie-downs, and check that the vent is clear.

Water loss is a common maintenance issue in wet-cell marine batteries, with deep-cycle batteries losing water faster than starters. Water loss often occurs in batteries from evaporation due to heat and other chemical reactions and can rapidly shorten your battery’s life. If you have a maintainable battery, top up your battery’s water level with distilled water: tap water contains impurities that will accumulate inside the battery and cause issues. Make sure not to overflow the water level.

How do I jumpstart my boat battery?

Jumpstarting a marine battery is very similar to jumpstarting a car battery. The main difference is that you need to ensure there is plenty of ventilation before connecting the battery: make sure to avoid fuel fumes.

After turning off all electrical appliances that use your boat’s battery, use a reliable jump-starter like the IS-1500. Attach the red clamp on the positive terminal, then the black clamp on the negative terminal.  Check the display on IS-1500 and once displaying a green light, start the engine. Once the motor is running, disconnect the jump-starter.

If jumpstarting your marine battery yourself doesn’t work, it’s time to call RACV Marine.

How do I store my boat battery during the off-season?

If you’re putting your boat in storage, keep your battery in a cool and dry location. Use a multistage charger like SmartCharge to keep your boat battery topped up during the off-season, which will keep it well-maintained and maximise battery life.

Where do I get a marine battery?

If you need a new marine battery, RACV Marine’s mobile battery team can deliver to your home, boat ramp or docked boat anywhere in Greater Melbourne and Geelong. They have a range of batteries to fit a variety of boats and yachts, all designed to withstand rough conditions and coming with one- or two-year warranties. RACV Members also receive a $15 discount off the RRP of marine batteries from RACV.