Before we explore a deep cycle battery, it’s crucial to understand some basic battery concepts, such as what a cycle entails, what deep discharge means, and the implications of deep discharge batteries.
A complete cycle is defined as the process of fully discharging a battery and then fully recharging it. But what does ‘fully discharged’ entail? Discharge is quantified by how much capacity is drawn from the battery—the Depth of Discharge (DoD) represents the percentage of the battery’s capacity used in a single discharge.
DoD is inversely proportional to the State of Charge (SoC), where SoC represents the battery’s remaining capacity. Therefore, 100% DoD corresponds to 0% SoC.
With an understanding of the concepts of DoD and battery cycles, you might wonder what a deep discharge is. A deep discharge is defined as 80% to 100% of the battery’s capacity being discharged.
What is a Deep Cycle Battery?
Simply put deep cycle batteries, like those from Keheng, are designed for sustained deep discharges of 80-100% DoD. Does this mean that high-rate batteries cannot be used for deep discharge? The answer is nuanced; high-rate batteries *can* be used for occasional deep discharges but are not designed for it. A small number of deep cycles will not harm the battery (if maximum discharge and charge rates are strictly adhered to), but this is where battery design becomes crucial. Consistent deep cycling will significantly degrade a high-rate battery over time.
Types of Deep Cycle Batteries
In Sealed Lead Acid (SLA) batteries, electricity is generated through chemical reactions at the plates. High-rate batteries have many thin plates to increase surface area, facilitating rapid energy generation. Conversely, deep cycle batteries have thicker plates because the chemical reaction that generates energy penetrates into the plates, thus requiring thickness to withstand that reaction. Thin plates, common in high-rate and starting batteries, degrade quickly and are unsuitable for repeated deep discharges.
Two subcategories of deep cycle SLA batteries include deep cycle gel batteries and AGM (Absorbent Glass Mat) batteries. Gel batteries convert the electrolyte acid into a thick gel, making them less prone to spills. Gel batteries offer better heat dissipation and reduced off-gassing than AGM batteries, leading to superior long-term performance. A fiberglass mat is placed between the positive and negative plates in AGM batteries to stabilize the electrolyte. This mat stabilizes the electrolyte, reducing the risk of spills, and also improves electrolyte distribution by maximizing contact with the plate surface area, compared to traditional batteries.
Energy cells are used in lithium deep-cycle batteries. These cells are carefully designed to provide a sustained current over a longer period of time, making them well-suited for cycling and deep cycling applications. Furthermore, the battery management system (BMS) is critical, as it regulates the current drawn from the battery. Different lithium batteries offer varying degrees of protection, so reviewing the technical documentation and specifications for details is recommended.
Like Keheng’s, deep cycle batteries are available in various chemistries, voltages, and capacities, with 12V and 24V models being the most common.
Applications of Deep Cycle Batteries
Before selecting a battery, it is essential to understand the application’s power requirements, duration, and frequency of use. Typically, deep cycle batteries are used in cycling applications where the battery’s use is determined by the user.
For example, hospital medical carts rely on battery power when not connected to an outlet. In this scenario, the healthcare provider activates the battery by turning on the power on the cart. This application requires the battery to be used daily.
For many hours each day, deep cycle batteries are essential for providing stable power over extended periods. These batteries are designed for deep discharge and are ideal for applications requiring long-lasting power. A device that uses a battery with deep cycle characteristics is a cell phone. These batteries are designed to last all day on a single charge and are used daily, depending on the battery’s age. The battery is activated by turning on the phone or unplugging it from the charger. Typically, users allow their phone batteries to fully discharge before recharging, resulting in a Depth of Discharge (DOD) of 100% and a State of Charge (SOC) of 0%.
Deep cycle battery technology is also used in various other applications, including marine and recreational vehicles (RVs), electric mobility scooters, various electric vehicles, and solar energy applications. In contrast, high-rate batteries are typically used for backup or emergency situations. For example, elevator batteries provide emergency backup power during power outages while in standby mode, rapidly releasing much energy in an emergency. These batteries may even need to be replaced before they are ever used. Think of high-rate batteries as an insurance policy for electricity, providing a burst of power in an emergency. Deep cycle batteries, however, are reliable and provide stable power frequently, typically undergoing complete discharge cycles daily.
How long do deep cycle batteries last?
A key difference between lead-acid and lithium deep cycle batteries is their cycle performance. Compared to lead-acid batteries, lithium deep cycle batteries are less affected by discharge rates. This means that in deep cycle applications where discharge rates often exceed 0.1C (where ‘C’ represents the battery’s capacity), a lithium battery with a lower rated capacity can outperform an equivalent lead-acid battery. The lifespan of a deep cycle battery is measured in cycles rather than time. A lead-acid battery can provide approximately 200 cycles (based on 100% DOD until the capacity drops to 80% of its original value), while a lithium deep cycle battery can reach over 2000 cycles, ten times that of a lead-acid battery.
Properly Charging Deep Cycle Batteries. Proper charging is crucial for maximizing the lifespan and performance of the battery. The appropriate charging method depends on the battery’s chemistry, voltage, and capacity. Keheng offers two charging guides tailored for deep cycle batteries: one for lead-acid batteries and another for lithium deep cycle batteries. By following these charging guides, you can ensure a longer battery lifespan.
Deep Cycle Battery Series. Keheng offers two SLA (Sealed Lead Acid) deep cycle battery series: KDC for standard AGM (Absorbent Glass Mat) deep cycle batteries and KDG for deep cycle gel batteries. In addition, there are two lithium deep cycle battery series (KSL-SC (for series-connectable lithium batteries) and KSL-BT (for Bluetooth-enabled lithium batteries)) as well as a lithium energy cell series for building custom deep cycle lithium battery packs.
For more information about deep cycle batteries, please consult our other resources for more detailed information.