A Guide to Replacing Marine and Leisure Batteries

After a long, hectic week at the office, a relaxing weekend on the boat with the family will be the perfect antidote.

After packing up the car and driving to the marina, you finally get the kids and the groceries on the boat, put the key in the ignition and – nothing.

Not even a click. It’s Friday night, the marina’s service center is closed, definitely not the evening you had imagined.

We all take our marine and leisure batteries for granted, but they need proper care and a replacement from time to time, just like anything else.

Keeping your batteries in tiptop condition and knowing when and how to replace marine and leisure batteries is key to enjoying your boat or RV after that long work week.

That’s especially true with the hotter climates of Asia, Africa, and the Mid-East.

Whether it’s a marine battery or a leisure battery, read on for tips on maintenance and replacement.

Types of Marine and Leisure Batteries

Whether you are using your boat or your RV, the demands on the batteries are the same. In most cases, the same battery provides power to start the engine and, when the engine’s off, to provide reserve capacity to power things like lights, stereos, and refrigeration.

Larger boat’s electrical systems might also have a bank of batteries separate from the starting batteries to power accessory loads.

  • Flooded wet-cell lead-acid batteries have been around for 160 years. They are still providing good, robust service at reasonable prices.
  • With a maintenance-free design, using Absorbent Glass Matt (AGM) batteries in marine and leisure services makes good sense. In addition, AGMs are less sensitive to higher temperatures and work well in starting and storage applications.
  • Less common in marine use are Gel Cell batteries. Although leak-proof – they can be placed on their sides without risk – they are less tolerant of heat and overcharging.
  • Lithium batteries have come a long way but remain very expensive and problematic for marine use in the Southern Hemisphere’s heat. Strict charging requirements, heat sensitivity and, cost limit their use.

Battery Maintenence Tips

Keeping your batteries clean and corrosion-free is key to prolonging their life. Cleaning the battery posts, terminals, applying dielectric, non-conductive grease (or even petroleum jelly) on a regular basis gives better performance.

Battery terminal protectors provide added protection against the hot, humid conditions often found in Africa and Asia.

Assuring that the electrolyte in wet-cell batteries completely covers the cell plates is critical to prolonging their life. If it needs topping off, use distilled water, not tap water!

Finally, regularly charging lead-acid and AGM batteries, bringing them back to full charge and never draining them below 40% of capacity keeps your batteries happy!

Battery Health Diagnostics

The first step in checking the health of your batteries (lead-acid or AGM) is to bring them up to full charge and then let them rest for at least six hours. Letting them rest for 12 – 24 hours is ideal. That means don’t use them!

Next, you will be using your handy DC Voltmeter – and if you don’t have one, buy one. A good digital multimeter costs less than lunch, and you can find them at any auto parts store.

Otherwise, you’ll be paying a lot more than the cost of lunch for your local boatyard’s service staff to check your batteries for you.

Learning how to use the voltmeter will save you money, and it means you shouldn’t ever be caught short with dead or dying batteries again.

After taking off the battery leads, put the voltmeter’s red probe on the battery’s positive post and the black probe on the negative post. Note the reading, comparing it to these standards for lead-acid batteries (add .4 volts for AGM batteries):

  • 100% 12.73 volts
  • 80% 12.50 volts
  • 60% 12.24 volts
  • 40% 11.96 volts
  • 20% 11.66 volts

Since you know that your battery is fully charged, if its reading is less than 12.7 volts, you know your battery is failing and replacing it goes onto your to-do list.

Likewise, a reading of less than 10.5 volts on the voltmeter tells you that a cell has failed in the battery.

How to Replace Batteries

Other than being heavy – and on both boats and RVs all too often being in hard-to-access spots – replacing batteries is a snap.

Before removing the old battery, disconnect all the leads to the battery’s posts and tuck them safely aside. Unless you happen to know the size of the tightening nuts, an adjustable crescent wrench will do the trick.

Once everything is safely disconnected, carefully lift the battery out. Exercise due caution with any battery but particularly with lead-acid batteries. The electrolyte is largely sulphuric acid – very caustic – and capable of burning skin. Gloves and eye protection are highly recommended.

If you were satisfied with your current battery’s performance (before it failed), the usual course is to replace it with a comparable battery – same size, same reserve hours, same cranking amps.

An exact match isn’t required; be sure to get a battery of the right size with close to the same specifications. If in doubt, contact your battery supplier.

Since you are replacing your battery, it might be a good time to upgrade if the battery you are replacing is a non-maintenance free lead-acid battery.

Moving up to a safer, fully sealed, maintenance-free battery will pay off over the battery’s life.

Once your new battery is in place, put a thin layer of the dielectric grease on both the battery posts and the leads, then tighten everything back up. Then, you are back in business!

Keep Your New Battery Happy

Regular maintenance combined with periodically checking your battery’s health is key to not getting a nasty surprise the next time you go to use your boat or RV after a long week.

Making it a habit to never drain your leisure batteries below 40% of their amp-hour capacity will dramatically increase your batteries’ useful life.

Even in demanding marine environments like those throughout Africa and Asia, a boat battery should have a life expectancy of three to five years with good maintenance

Based on that, budgeting for a battery replacement schedule is a prudent course of action. That way, your weekends will be stress-free!