The Best Marine Battery Savers

Best Premium Choice

optima Battery Red Top Battery


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Best Budget Choice

Expert Power 12v 7ah Batteries


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Best Overall Choice

ACDelco 94RAGM Battery


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Chris Riley by Chris Riley Updated on January 4, 2022. In nauticalknowhow

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DISCLAIMER: The info we’re presenting here is based more on experience than verified technical details. If you’re not comfortable wiring a 12 volt marine battery on your own, consider getting a professional to handle this kind of work instead.

What Are Deep Cycle Marine Batteries?

The deep cycle batteries or battery banks usually found in cruising boats were designed for deep cycling. This may seem rather obvious but it turns out that if you don’t deep cycle them you can destroy them. This is no problem when you are cruising away from shore power but for those long stays at the dock you need to take protective measures.

Deep cycling means you can use these batteries over the long haul. You should use them until they’re around 80% depleted and only then recharge them again. Some manufacturers recommend not discharging them that far and instead suggest that, when there is 45% charge left that they be recharged. This will greatly extend the battery life.

With a battery charger maintaining a constant voltage, those intermittent loads such as flushing a toilet or running a water pump take just a tiny charge off the top of the battery capacity which is replaced in a few minutes by the charger. This short cycle, always at the same place on the battery plates, can produce a layer which can materially reduce the capacity of your expensive battery bank and shorten its life drastically.

This means that, while it may seem like a good idea to keep your battery topped up all the time, it can ruin a deep cycle battery. If you keep charging it when it’s barely lost a charge, you may in fact be lowering the overall lifespan each time you do.

How to Save Your Deep Cycle Batteries

Banshee LiFeP04 Deep Cycle Battery 100Ah 12V

there are two solutions. One is to turn off your charger until the bank is about 20% discharged so that the battery is not short cycling at the same spot. This has the problem of remembering to turn it back on and also that you are using up the cycle life of your expensive battery bank.

A much better solution is to completely disconnect the battery bank from your system and replace it with a regular automotive starting battery. These batteries are designed to operate in this manner and one small battery is adequate for supporting those intermittent 12 volt loads with the help of the on line charger. Nowadays you can purchase a suitable marine starting battery for a decent price with a 3 to 5 year life guarantee. You probably are voiding the warranty by using it on a boat but you will be getting a battery that will support the load for many years at minimal cost.

Marine supply stores sell an economical single-pole battery switch that makes the changeover simple. Put one in series with the battery being isolated so it can be disconnected. Leave the cheapo 12 volt in circuit all the time – it adds a little extra capacity.

If your (now) isolated house battery is of the maintenance free type, it can be left idle for long periods with no significant loss of life but you should put them back on charge once or twice a year to keep them ready. If they are the lead-acid type, you will need to check the voltage more often.

One more thing to remember is temperature extremes. If your boat is down south all year this may be less of a concern. But we’ve all seen snow in Texas and Florida in recent years and now how unpredictable the weather can be. Most deep cycle batteries do not respond well to freezing temperatures. Storing them indoors can really help in maintaining batteries over the winter

Before you store your battery and boat for a season, you want to make sure your deep cycle marine battery has a full charge. Remember, long life is what this battery was designed for. When not in use, the rate of discharge is quite low. You shouldn’t need to keep a charger plugged in all the time to keep this kind of battery alive. And if you’re storing it over the winter, you should only need to check in once in a while to see how it’s doing. It’s not uncommon to only lose around 20% charge.

Charge Your Deep Cycle Batteries Properly

Even with the backups we’re suggesting, you still need to care for your main battery. The best way to do that is to make sure you’re charging it the right way. Typically, these batteries are charged one of two ways. The first is a full cycle charge. That means every day you’re using it you allow it to come to a full charge afterwards when you’re done using it. So you allow the battery to deplete, and then you fully replenish.

The other way of charging is what is called opportunity charging. This is a bad habit but most of us are guilty of it now and then. You forget about the battery, you plug it when you think of it, and then stop charging it when you need it again, then plug it back in to charge later. This is convenient for most of us but it plays havoc with the battery internally. It will seriously reduce the overall lifespan of the battery when it’s operated this way.

Best Marine Battery Savers

If you’re looking to follow our advice and wire an automotive battery in line to save your marine battery, there are plenty of choices. Here are the three of the best marine batteries we think are the best to keep your marine battery in good working order for as long as possible.

Best Premium Choice

1. optima Battery Red Top Battery

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The best of the best when it comes to automotive starting batteries. The reserve power is up to 100 minutes, meaning it works well beyond just being a starter. It can stand up to abuse and is designed for heavy use. This thing is built with extreme durability in mind. It also handles temperature extreme wells, which can be a real blessing on a boat.

So why are we recommending another deep cycle battery as a starter battery anyway? Because this is designed to do both and it does it incredibly well. The initial burst of power produced by the Optima is arguably the most reliable of any battery on the market. And the follow up lifespan is second to none. Make no mistake, it’s a premium battery but it does the job so much better than much of the competition.

The science behind the battery is what makes it so reliable. Most batteries use lead sheets. They have impurities and are less reliable, relatively speaking. Optima uses coiled lead columns. This lowers the ohms but increases energy output. It also makes the battery more stable overall. You can expect it to last upwards of twice as long as conventional batteries.

Weighing just under 39 pounds, it offers 800 cold-cranking amps. You can mount it in nearly any position. These are designed to handle heavy duty work in trucks and performance automobiles. That means the intermittent needs of your boat will be well taken care of by the Optima and, with its power reserves, even if something goes amiss you’ll be fine. These aren’t the cheapest option by any means, but if you want solid performance that preserves your marine battery, give it a look.

You may also want to check out Optima’s Blue Top battery which is designed specifically as a marine starter battery. We think the Red Top works a little better overall as the Blue Top is designed to never be used for cycling duty. It really depends on how you intend to use your batteries.

Optima offers a 3-year guarantee on their batteries, so there is some peace of mind with the pricetag.

Best Budget Choice

2. Expert Power 12v 7ah Batteries

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When you’re looking to save a few bucks, you can get creative. As long as you know your wiring setup, or have a pro do it, consider using something like these Expert Power scooter batteries. These batteries, or golf cart batteries, can be wired together to provide enough power at a fraction of the cost of normal batteries.

One thing you need to be aware of though is how your charger works. If you have a charger that is rated for 12v batteries at something like 20ah to 80ah then you’ll need to make sure you have enough of these smaller batteries wired together in a pack. In this case, 3 of these 7ah batteries can charge together as 21ah and your charger will not damage them, so keep that in mind.

With over 15,000 reviews on Amazon, you can count on Expert Power’s batteries to get the job done. These aren’t full car batteries, but they’re reliable and they have a long life. When you need that extra boost and don’t want to drain the house battery, these are a great and affordable option.

They’re easy to use and easy to set up. The cases are surprisingly durable, but we don’t recommend you put them through any more abuse than is necessary. These are some value options, after all, and they’re not built as tough as the Optima or the ACDelco by any means.

They come with a 90-day money back guarantee and a 1-year warranty for quality.

Best Overall Choice

3. ACDelco 94RAGM Battery

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ACDelco offers up an impressive 800 cold cranking amps here and a ton of power. If you’re boating anywhere that has to endure frosty cold mornings, you’ll be thankful for this battery. Weather extremes are what this was built for.

This is an AGM or absorbent glass mat battery, as opposed to a lead acid battery like some cheaper ones. The difference is AGM batteries are maintenance free. No gasses like those produced in flooded lead acid batteries are produced. That means it can be stored in a sealed area, even under a seat. These batteries are also built tougher. That’s not just an opinion, they were literally designed for military and aviation use. They’re meant to handle more shocks and vibrations.

With a 36-month replacement warranty you can rest easy that the battery isn’t going to crap out on you too early. And, if we’re being honest, it probably won’t come to that anyway. These are some of the most robust and powerful batteries on the market. In most cases you can expect the lifespan to well outlive that warranty, but obviously it’s nice to have that just in case.

The case has been pressure tested and is designed to handle extreme shock without damage. You never want to beat up your battery, but we all know accidents happen. Things can get unpredictable on a boat, so that makes this an excellent choice if you’re looking to be prepared for anything.

The battery cell is silver-calcium, something you won’t see in a lot of other batteries. That’s going to offer not just longer life but better overall performance. You’re looking to maximize the overall electrical abilities of your boat, so this is a great pairing for your deep cycle battery.

The Bottom Line

Boat electronics can be finicky and not all of us like to run things the same way. You may only need your battery for the bare minimum with your lights or VHF radio. Other boaters like to have all manner of electronic devices from microwaves to televisions and more running. So the electronics needs for powering onboard accessories can vary significantly from one vessel to the next. But regardless of what you’re doing, you still need to take proper care of your battery. Protecting it and making sure it has the longest lifespan it can have just makes sense, right?

Always make sure you’re following proper procedures for charging a marine deep cycle battery. Never use a charger not rated for your battery type, and make sure you’re getting a full charge each time you charge, but also discharging as far as is recommended each time as well.

If you’re doing any wiring with your boat batteries, make sure you’re confident you’re doing it the right way. If you’re new to this kind of wiring, don’t be afraid to ask for help. Better to call in the assist to make sure it’s done right then to struggle through having nothing work at all or, worse, losing power when you’re out on the water.

As always, stay safe and have fun.

About Chris

Outdoors, I’m in my element, especially in the water. I know the importance of being geared up for anything. I do the deep digital dive, researching gear, boats and knowhow and love keeping my readership at the helm of their passions.


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