Deep-cycle battery

A deep-cycle battery powering a traffic signal

A deep-cycle battery is a battery designed to be regularly deeply discharged using most of its capacity. The term is traditionally mainly used for lead–acid batteries in the same form factor as automotive batteries; and contrasted with starter or cranking automotive batteries designed to deliver only a small part of their capacity in a short, high-current burst for starting an engine.

For lead–acid deep-cycle batteries there is an inverse correlation between the depth of discharge (DOD) of the battery and the number of charge and discharge cycles it can perform; with an average depth of discharge of around 50% suggested as the best for storage vs cost.

Newer technologies such as lithium-ion batteries are becoming commonplace in smaller sizes in uses such as in smartphones and laptops. The new technologies are also beginning to become common in the same form factors as automotive lead–acid batteries, although at a large price premium.

Types of lead–acid deep-cycle battery

A deep-cycle battery hooked up to a charger

The structural difference between deep-cycle and cranking lead–acid batteries is in the lead battery plates. Deep-cycle battery plates have thicker active plates, with higher-density active paste material and thicker separators. Alloys used for the plates in a deep-cycle battery may contain more antimony than that of starting batteries. The thicker battery plates resist corrosion through extended charge and discharge cycles.

Deep-cycle lead–acid batteries generally fall into two distinct categories; flooded and valve-regulated lead–acid (FLA and VRLA), with the VRLA type further subdivided into two types, absorbent glass mat (AGM) and gel. The reinforcement of absorbed glass mat separators helps to reduce damage caused by spilling and jolting vibrations. Further, flooded deep-cycle batteries can be divided into subcategories of tubular-plated opzs or flat-plated. The difference generally affects the cycle life and performance of the cell.

Flooded

The term flooded is used because this type of battery contains a quantity of electrolyte fluid so that the plates are completely submerged. The electrolyte level should be above the tops of the plates which serves as a reservoir to make sure that water loss during charging does not lower the level below the plate tops and cause damage. Flooded batteries will decompose some water from the electrolyte during charging, so regular maintenance of flooded batteries requires inspection of electrolyte level and addition of water. Major modes of failure of deep-cycle batteries are loss of the active material due to shedding of the plates, and corrosion of the internal grid that supports active material. The capacity of a deep-cycle battery is usually limited by electrolyte capacity and not by the plate mass, to improve life expectancy.

1. Plate Design

• Deep Cycle Batteries: One of the biggest differences in the construction of deep cycle batteries lies in the plates inside the battery. These plates are typically thicker and denser than those found in starter batteries. This design allows the battery to handle deep discharges—that is, the ability to provide power over a long period, draining up to 80% of its capacity without damaging the battery.
• Starter Batteries: In contrast, starter batteries have thinner plates that are designed to provide a large surge of current for a short period, such as when starting an engine. These thinner plates allow the battery to charge faster, but they aren’t built to withstand deep discharges and prolonged use.

Why this matters: The thicker plates in deep cycle batteries enable them to endure many more charge-discharge cycles compared to starter batteries. They are designed to provide a steady output over long periods, whereas starter batteries are optimized for quick bursts of high power.

2. Active Material Composition

• Deep Cycle Batteries: The active materials (lead and lead oxide) in deep cycle batteries are formulated for durability and extended use. These materials are packed into the plates more densely, which helps increase the battery’s overall energy density and ensures it can withstand frequent discharging and recharging.
• Starter Batteries: The active materials in starter batteries are designed to deliver a quick, powerful current to start an engine, but they wear out faster when subjected to deep discharges. As a result, starter batteries use a more loosely packed composition to optimize for instantaneous power.

Why this matters: A deeper cycle means more charge and discharge cycles over a battery’s life. Deep cycle batteries are built with materials and components that are more resistant to wear and capable of enduring repetitive cycling.

3. Battery Construction (Flooded vs. Sealed)

• Flooded Deep Cycle Batteries: The most traditional deep cycle batteries are flooded lead-acid batteries (FLA), where the plates are submerged in a liquid electrolyte (sulfuric acid and water). These batteries require maintenance, such as topping up with distilled water to compensate for evaporation, especially if they are used frequently or in high temperatures.
• Sealed Deep Cycle Batteries: More advanced deep cycle batteries, such as AGM (Absorbent Glass Mat) and gel batteries, are sealed. These use a special gel or fiberglass mat to absorb the electrolyte, eliminating the need for regular maintenance. They also tend to be more resistant to vibration, making them ideal for marine or off-road applications.
• Starter Batteries: Starter batteries can also be flooded or sealed, but flooded starter batteries are often used in applications where maintenance is less of an issue, like in cars, and where battery life is generally shorter due to the high power bursts required for engine starts.

Why this matters: The construction of the battery impacts its maintenance needs, durability, and safety. Sealed deep cycle batteries, for example, require little to no maintenance and are less prone to leaking, making them ideal for applications where maintenance accessibility is limited (like in an RV or a boat).

4. Battery Capacity and Voltage

• Deep Cycle Batteries: Deep cycle batteries are designed to have a high capacity (measured in amp-hours, or Ah) and are often rated to handle deep discharge cycles. They typically have a lower voltage drop over time, meaning they provide a consistent power output until they are almost empty.
• Starter Batteries: Starter batteries generally provide higher peak amperage (measured in cold-cranking amps, or CCA) but only for short bursts. Their capacity is lower because they don’t need to provide power for extended periods, but they are optimized for delivering instantaneous high currents to start an engine.

Why this matters: For an application where you need to run appliances, lights, or other equipment over several hours or days, the deep cycle battery’s high capacity and ability to maintain a steady voltage are essential.

5. Battery Case and Internal Construction

• Deep Cycle Batteries: The battery case for deep cycle batteries is typically reinforced and built to handle the stresses of frequent charging and discharging, as well as the physical demands of harsh environments (e.g., marine, off-road, or solar installations).
• Starter Batteries: Starter batteries often have a more lightweight design and a case that’s optimized for vehicle installations. They are built to be compact, as space is often at a premium in cars and trucks.

Why this matters: A robust, heavy-duty construction ensures deep cycle batteries can handle the physical challenges of their applications without breaking down prematurely.

OPzS batteries

OPzS stands for German ortsfest Panzerplatte, Säure, stationary tubular plate, acid.

OPzS batteries are a type of deep-cycle battery commonly used for backup power systems and renewable energy applications. OPzS is recommended for storing energy from intermittent supplies, such as wind and solar supplies for off-grid use.

OPzV batteries

OPzV stands for ortsfest Panzerplatte, verschlossen, meaning stationary tubular plate, sealed.

OPzV batteries are very similar to OPzS batteries, with the only technical difference being that OPzV batteries are sealed. OPzV batteries are relatively maintenance-free, while OPzS batteries require the occasional top-up with distilled water.

New technologies

Although still much more expensive than traditional lead–acid, a wide range of rechargeable battery technologies such as lithium-ion are increasingly attractive for many users.

Applications

Deep-cycle batteries in an electric boat refit

• Cathodic protection, which might include marine use
• Other marine use, especially on a sailboat lacking power generation capability, generally smaller vessels
• Trolling motors for recreational fishing boats
• Industrial electrically-propelled forklifts and floor sweepers
• Motorized wheelchairs
• Off-grid energy storage systems for solar power or wind power, especially in small installations for a single building or motorhome
• Power for instruments or equipment at remote sites
• Recreational vehicles
• Traction batteries to propel vehicles, such as golf carts, and other highway electric vehicles
• Traffic signals
• Uninterruptible power supply ('UPS'), usually for computers and associated equipment, but also sump pumps
• Audio equipment, similarly to a UPS but also in certain 'clean power' devices to supply clean DC power isolated from the public electric supply for inversion to AC to maximize audio signal reproduction

Recycling

According to the Battery Council International (BCI) – a lead–acid battery industry trade group – the vast majority of deep-cycle batteries on the market today are lead acid batteries. BCI says lead acid batteries are recycled 98% by volume, 99.5% by weight. According to BCI, the plastic cases, lead plates, sulfuric acid, solder, and other metals are 100% recovered for reuse. BCI says the only part of a battery that is not recyclable is the paper separators that wrap the plates (due to the acid bath the paper sits in, the fiber length is reduced so far that it cannot be rewoven).

BCI says that, industry wide, there is a greater than 98% rate of recovery on all lead acid batteries sold in the United States, resulting in a virtually closed manufacturing cycle.

See also

• Desulfation
• Electric vehicle battery
• List of battery types
• Peukert's law

External links

• The difference between deep-cycle batteries and regular lead–acid (car) batteries at HowStuffWorks
• Battery Council International
• Car and Deep-Cycle Battery FAQ 7.0