What Is a Deep Cycle Battery? Amp-hours, Cycling and More

Did you know your car battery only works for about 10-20 seconds and then sits back until it’s recharged to 100%? Usually, it can start your engine in less than 10 seconds, draining only 3%-8% before needing to recharge, and that’s a full workday for a car battery. It’s made to give a burst of electricity — and if you draw more power than that (by leaving the headlights on), you could damage or outright kill your car battery.

Sometimes you need more than 30 seconds of electricity.

Deep cycle batteries can give a steady electrical current and drain down to just 20% and recharge without damage. A deep cycle battery’s power is typically measured in amp-hours (Ah), as in how much power it can deliver in 20 hours. These batteries come in different types, with chemistries from regular, flooded lead-acid batteries to enhanced flooded batteries to the absorbed glass-mat batteries. Different in design from car batteries, a deep cycle battery’s lead plates and a special chemical paste on the plates allow it to store hours of amperage and recharge fully without damaging its storage capacity. That’s cycling — and the more you drain the battery, the “deeper” the cycle.

Cycles are easier to understand when you apply it to your phone. Every time you drain your phone and recharge it, your phone battery goes through one cycle. A deep cycle, then, is when your battery drains to 80% before you recharge it again. That can put a lot of strain on a battery, unless it was made for it. A deep cycle battery is engineered for repeated deep cycles without wearing down easily.

These batteries come in various group sizes, voltages and chemistries because they have so many uses.

What’s a deep cycle battery usually used for?

Any time you want electrical power, but you don’t have a generator or alternator handy, you’ll usually need a deep cycle battery.

Deep cycle batteries are your powerhouse for electronics and gadgets when you’re on the water, off the grid, off the beaten path, etc. A deep cycle battery can deliver a lot of amperage before it needs to be recharged, making it ideal for golf carts, RV power banks, boats or even solar panel arrays. Some deep cycle batteries have enough cranking power to start a boat motor, depending on their cold cranking amps or CCA rating. That said, usually when you’re shopping for a deep cycle battery, you’re looking at the amp-hour rating or Ah rating.

Let’s go through the most common types of deep cycle battery applications.

Deep cycle marine batteries

Deep cycle marine batteries can make or break a fishing trip. These powerful batteries usually run trolling motors, fish finders, coolers, antennas, anything you might want for a day on the water. If you’re taking the boat out for the weekend, this is the battery powering any boat lights, stereo or laptops. Depending on your boat and setup, you may have just one or a couple wired in parallel (for double the amps).

In a pinch, a fully charged deep cycle battery could start a boat motor. However, its real advantage lies in keeping phones charged and fish finders finding fish.

Deep cycle golf cart batteries

Deep cycle golf cart batteries keep these quiet electric carts moving up and down neighborhoods and golf courses, only to be recharged on the off hours so they can do it the next day. Golf carts can require up to 48 volts, drawn from six or eight batteries connected in series (so their voltage builds up.) Deep cycle golf car batteries are made for either 6 volts or 8 volts and can deliver substantial amperage compared to marine batteries.

Deep cycle RV batteries

Deep cycle RV batteries deliver the house power that makes a trip in the RV fun between electrical hookups. Coffee makers, refrigerators, phone chargers, cooking equipment — anything not running from the RV’s alternator is drawing power from a bank of deep cycle batteries. The house power delivers all the creature comforts — and then recharges from the RV’s alternator.

RVs can use either golf cart batteries or marine batteries, depending on the recreational vehicle’s electrical system and how much power you need. A typical RV may run on half a dozen 12-volt deep cycle RV batteries or at least two deep cycle golf car batteries with 6 volts each. Usually, an RV doesn’t have just one deep cycle battery for house power.

Amp Hour Ratings: What are amp hours on a deep cycle battery?

A deep cycle battery can give a lot of power over time. But how much?

The amp hour (Ah) rating is one way of measuring the power of a battery designed to give a lot of power over time. Specifically, the Ah rating shows how many amps a deep cycle battery can give in 20 hours.

If you have a battery with 200 Ah, that means it can give 10 amps for 20 hours. Most car batteries have a low Ah because they’re not designed to deliver sustained current over a long period of time. On the other hand, a deep cycle marine battery designed with 100 Ah can run your 5-amp coffee maker for 20 hours.

But who runs their coffee maker that long?

Most deep cycle batteries have labels that show another power rating: Reserve capacity or RC. Reserve capacity shows how many minutes this battery can give you 25 amps of power. If your deep cycle marine battery has a reserve capacity rating of 180, that means it can give you 25 amps for three hours.

Regular, EFB or AGM Deep Cycle: What’s the Best Deep Cycle Marine Battery?

Do you need an absorbed glass-mat (AGM) battery, an enhanced flooded battery (EFB), a maintenance-free battery or a standard lead-acid battery? The best deep cycle marine battery depends on precisely the application and how you plan to maintain it.

• Do you need hours and hours of a few amps, or some substantial amperage all at once?
• Will you be able to maintain and check its water levels, or will you leave it to charge and not think about it?
• Are you hoping for a deep cycle battery that can pinch hit as a cranking battery?

AGM deep cycle batteries

Capable of both deep cycling and cranking, an AGM deep cycle battery like the Interstate Marine/RV 34M is the best battery when you’re looking for a versatile powerhouse. Its performance comes from the fact that, instead of free-flowing liquid inside, its lead plates are packed inside of fiberglass mats soaked with the acid that conducts the electricity. Because AGM batteries are sealed, they don’t require any maintenance aside from charging with a specific kind of charger. They deliver a lot of power for their weight and how much floorspace they take up.

The best deep cycle marine battery is an AGM for anyone who wants both a starting battery and a deep cycle but doesn’t want to carry around two batteries. That’s why we call them dual purpose marine/RV batteries.

EFB deep cycle batteries

With a power profile that’s tipped toward cycling, an EFB delivers a noticeably longer lifespan than a traditional flooded deep cycle battery. They can perform like an AGM battery with significant differences. While they’re sealed, they still have loose, free-flowing liquid inside. However, a tight-knit weave design and special chemical additives allow this lead-acid battery to outperform its maintenance-free cousins and keep up with the advanced AGM design.

EFBs make the best deep cycle marine battery when you’re running a lot of power all day long and you plan to recharge them all night.

Maintenance-free deep cycle batteries

You may have heard the phrase “maintenance-free battery” and thought, “Isn’t that just recharging a battery?” Well, recharging is one part of maintaining a deep-cycle battery — but it’s not the whole story.

Typically, a lead-acid battery loses a small amount of water every time it’s used or whenever it gets hot. Losing water can dry out the sensitive components unless the battery is sealed and chemically formulated to protect them.

That is, unless you’re using a maintenance-free battery. These sealed-top deep cycle batteries have a special series of one-way air valves that protect the battery. Essentially, you can’t add water and you don’t need to, unless you overheat the battery when you recharge it.

This is the best deep cycle marine battery for the casual boater and fishing fan. Set it on a trickle charge all winter long, and by spring, it’ll be spruced up and ready for the lake.

Lead-acid deep cycle batteries

These deep cycle batteries are like a regular car battery except designed for deep discharging and recharging. They’re filled with free-flowing liquid and have removable caps so that you can take a hands-on approach to maintaining your battery. Watering your battery is especially common for deep cycle batteries such as golf cart and marine batteries that get drained and recharged on a regular basis.

These batteries are ideal deep cycle marine batteries for someone who needs to make a little bit of power stretch a long time.

How Long Do Deep Cycle Batteries Last?

Deep cycle batteries have a slightly longer lifespan than regular car batteries, between three to six years.

A deep cycle battery’s service life can vary depending how well maintained it is and how well it was treated before you bought it, just like a typical car battery’s lifespan. Both EFB and AGM deep cycle batteries can generally stay in service much longer than a regular deep cycle battery, all things being equal.

Now, if it’s a deep cycle battery with removable filler caps, it’s entirely possible to keep that battery working much longer than six years. That is, if you never leave it fully drained. All it takes is one Saturday left on the bench, all drained and waiting for a recharge for the battery to become seriously damaged.

How to Make Deep Cycle Batteries Last Longer

Maintaining deep cycle marine batteries takes three simple steps.

1. Recharge your deep cycle batteries often to keep them well-charged. Use a battery charger designed for your battery’s technology, whether it’s AGM, EFB or a simple sealed lead-acid battery. To protect your battery, set a charging rate less than 3 amps. See your specific battery’s manual for specific charging times. If you don’t have it handy, you can also take your battery’s Ah and divide it by 10 to get the charging rate. (Be sure to always charge your lead-acid batteries in a well-ventilated area.)

   Check your batteries’ power regularly. Try to keep your deep cycle batteries as fully charged as often as possible. Lead-acid batteries will weaken if they are left for days at less than 80% charge, even deep cycle batteries. Their active material (the parts that store electricity) goes inert if they’re left discharged too long. That’s called sulfation and essentially it cuts into how much power a battery can store.

   Want a neat pro tip? The liquid inside your battery will appear clear like tap water if it’s fully charged. If it’s drained, the liquid inside will be cloudy, yellow or green in color.

Protect your deep cycle battery with the Interstate Guardian

Available at an Interstate All Battery Center near you, the Guardian charger from Interstate can charge AGM, EFB and regular lead-acid batteries.

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2. Protect your batteries from heat by recharging them slowly and watering them. A full day running the trolling motor won’t damage your deep cycle marine battery; a full day sitting in direct sunlight could. Heat damages batteries permanently and can eventually kill them.

   While charging batteries keeps them healthy, charging also can overheat them. Hot batteries can lose water, which can also cause sulfation. EFB and AGM batteries use a different kind of charger than a typical deep cycle battery to charge carefully. A smart charger that can transition to a trickle charger will protect your marine batteries a long time.

   What about golf cart batteries or marine batteries with vent caps you can open? You can refill deep cycle batteries with distilled water to replenish the lost water from recharging and regular use. After opening the top, you’ll see a fill line on the edge. Add enough distilled water to one-eighth of an inch over the lead plates inside. Always remember to use distilled water; any impurities can cause problems for your battery’s sensitive internal components.

3. Clean the battery terminals and connections. Dip a brush in a mixture of baking soda and distilled water. Then carefully brush the corrosion away.

   As batteries deliver power and recharge, corrosion builds up around the terminals and any cables. Corrosion chokes the flow of electricity, making your battery work harder and making it harder to recharge. If left too long, corrosion can also damage the clamps that connect to the battery posts.

   You can use a battery post cleaner and a corrosion preventative spray to protect your deep cycle marine batteries.

Check your batteries’ labels and owner’s manual for the most complete maintenance instructions for your specific batteries. Exercise caution when handling, charging, activating or installing batteries. Always wear protective gloves and eyewear when working with batteries.