How To Charge a Deep Cycle Battery

Are you trying to decide whether a deep cycle battery is right for you or wondering how to optimize performance when charging one you already have?

It’s essential to know how to charge a deep cycle battery safely — and with its long-term health in mind. 

In this article, you’ll learn:

• What a deep cycle battery is 
• Why deep cycle batteries are useful
• The most common types of deep-cycle batteries
• How long do deep cycle batteries take to charge
• The best way to charge a deep-cycle battery

And more!

Whether you’re considering installing an off-grid solar power system in your home or wondering how to power your RV, deep-cycle batteries are the best choice.

Charging deep cycle batteries the right way correctly is vital for safety, longevity, and optimizing long-term performance. 

What Are Deep Cycle Batteries? 

Before diving into how to charge a deep cycle battery in detail, let’s cover what it is.

To understand what sets deep cycle batteries apart from other rechargeable batteries, you must grasp the concept of depth of discharge. 

All batteries have a storage capacity that indicates how much electricity they can store with a full charge. 

For example, EcoFlow DELTA Pro offers 3.6 kWh of storage capacity when fully charged. 

Depth of discharge refers to the percentage of a battery’s total storage capacity that’s been consumed. 

Again, using EcoFlow DELTA Pro as an example, if you consumed 500 watt-hours of its 3.6kWh capacity, the unit’s depth of discharge would be about 13.9%. That means you’ve used about 13.9% of the battery’s total storage capacity.

Pretty simple, right? 

But here’s where it gets a bit more tricky: 

Different batteries have different recommended depths of discharge. The recommendations can vary hugely, primarily based on battery chemistry. 

Discharging the battery below its recommended depth of discharge (DoD) can permanently damage the battery and significantly shorten its lifespan. 

Lead acid batteries tend to have a recommended depth of discharge of around 50%. Using more than 50% of a lead acid battery’s total storage capacity can lead to permanent damage. 

Effectively, the usable storage of a 3.6kWh lead acid battery with 50% recommended DoD is only 1.8kWh.   

In comparison, lithium-ion batteries typically have a DoD of around 80%. Lithium iron phosphate (LiFePO4) batteries, like those used in EcoFlow portable power stations like EcoFlow DELTA Pro, can offer an even greater depth of discharge. 

The recommended depth of discharge is essential to consider when choosing a battery that will meet your needs. Batteries with a shallow depth of discharge often have a lower sticker price, but their usable storage and lifespan are usually inferior to more costly options. 

Deep cycle batteries are designed to be discharged “deeply” on a regular basis and use more of their storage capacity without fear of damage. Deep cycle batteries are superior in applications that require frequent charging and discharging during normal use.

Examples of applications where deep cycle batteries are beneficial include:

• RV power
• Boat power
• Home battery backup power
• Off-grid solar panel systems
• Solar generators 

In such applications, it’s easy to see how useful it is to be able to discharge more of your unit’s available capacity safely.

Common Types of Deep Cycle Batteries

Batteries that claim to be “deep cycle” are mostly commonly either:

• Flooded lead acid (FLA) and 
• Valve-regulated lead acid (VRLA) 
• Nickel-cadmium (Ni-Cad)
• Lithium-ion and newer subsets of Li-ion, like:
  • Lithium nickel manganese cobalt (NMC)
  • Lithium iron phosphate (LiFePO4/LFP)

Lead acid and Ni-Cad rechargeable battery chemistry dates back to the 1800s. For decades, these were the only options.

Lithium-ion batteries are a relevantly recent innovation available since the 1990s and are the better rechargeable battery option for most applications.

Here are some primary benefits of lithium-ion deep cycle batteries compared to lead acid and Ni-Cad.

• Greater depth of discharge
• Consistent voltage output during a cycle
• Higher potential AC and DC electricity output

Lithium-ion — and particularly LiFePO4 — deep cycle batteries are the first choice for modern off-grid backup power and solar panel systems.  

How Long Does It Take To Charge a Deep Cycle Battery? 

How long a deep cycle battery takes to charge varies significantly based on numerous factors, including:

• Battery Chemistry
• Total storage capacity
• Charging method (Solar, fossil fuel, DC, etc.)
• Current depth of discharge (Is the battery 50% or 0% charged?)
• Quality and efficiency of complementary components like inverters, charge controllers, and Battery Management systems

Because there are so many types of deep cycle batteries for so many applications, no definitive time for how long it takes to charge one can be given. However, manufacturers will usually provide estimates of how long each battery model will take to recharge based on the charging method and other factors.  

How Long Do Deep Cycle Batteries Last Without Charging? 

Again, the answer is…

It depends.

How long your deep cycle battery will last between charges depends on numerous factors, including:

• Usable storage capacity
• Electricity consumption
• Age and condition
• Temperature (Operating and charging) 
• Charging method
• Depth of discharge
• Battery Chemistry
• Quality of manufacture 

How Long Do Deep Cycle Batteries Hold a Charge When Not in Use

If you’re wondering how long a deep cycle battery holds a charge in storage or with minimal use, it again varies due to many of the factors mentioned above.

New lead acid deep cycle batteries can typically hold a charge for 3-6 months if kept in optimal conditions. Depending on the type of lead acid battery, you may also need to monitor water levels. The actual time a lead acid battery can hold a charge in storage depends primarily on its self-discharge rate.

It’s a best practice to charge lead acid batteries periodically or use a trickle charger or battery maintainer. Even if you’re not using the battery currently, taking these steps can extend its lifespan and ensure optimal performance. 

Lithium-ion and LiFePO4 batteries have a much lower self-discharge rate than lead acid and can typically retain 80-90% of their charge even after being idle for 3-6 months.

Still, it’s good practice to use and recharge your Li-ion deep cycle batteries at least once every six months.

What is the Lifespan of a Deep Cycle Battery?

The lifespan of a deep-cycle battery depends primarily on battery chemistry and frequency of use.

Lead acid batteries are significantly more subject to degradation over time and without adequate maintenance than lithium-ion and LiFePO4 alternatives. However, properly maintained lead acid deep cycle batteries can still last 5-10 years, depending on their use.

Cycle life is a far better measure of deep cycle battery longevity than time. Both lead acid and li-ion batteries diminish more in performance with use than with age.

A battery cycle is one complete charge/discharge. Cycle life measures how many times a battery can be discharged and discharged before its performance decreases — or it stops working altogether.

Again, cycle life varies widely with battery chemistry, application, and quality of manufacture. 

Deep cycle lead acid batteries typically average 200-1,000 cycles before their performance and storage capacity noticeably diminish — usually to about 80%. Capacity will continue to decline until the battery is dead.

On the other hand, the LiFePO4 batteries in EcoFlow’s portable power stations and solar generators have a cycle life of 3,500 cycles to 80% capacity and  6,500 cycles to 50% capacity. 

That’s more than triple a high-quality lead acid deep cycle battery — good for a decade of daily use. 

How Should a Deep Cycle Battery Be Charged? 

Depending on the application, your deep cycle battery may offer multiple charging options or only one. 

The best way to charge a deep-cycle battery depends on the available charging methods and the manufacturer’s instructions. 

For example, the deep cycle LiFePO4 batteries in EcoFlow’s off-grid power solutions offer a minimum of four charging options:

• Solar panels
• AC (Household electricity)
• DC (Car adapter)
• USB-C 

Models like the EcoFlow DELTA Pro offer additional charging methods — including EV charging stations.

EcoFlow’s portable power stations, solar generators, and Power Kits.

One of the primary benefits of using one of EcoFlow’s off-grid power solutions is that you get all of the advantages of a deep cycle LiFePO4 battery with sophisticated protective components built-in, including:

• DC to AC solar inverter
• MPPT charge controller
• Advanced battery management system

By opting for a plug-and-play deep-cycle battery solution with multiple charging options, you automatically see many of the pitfalls that can arise with other deep-cycle battery options.

Here are some steps you can take to help ensure your deep cycle battery’s safety, longevity, and optimal performance. Thanks to EcoFlow’s innovative design, these don’t all apply to their products, but they’re valuable rules of thumb.

• Always follow the manufacturer’s instructions
• Do not overcharge or undercharge the battery
• Only charge or operate the battery in the manufacturer-specified temperature range and conditions  
• Perform routine maintenance as required (especially for lead acid batteries)
• Periodically use the battery and recharge it. Don’t let it sit forever on a shelf
• Only use the charger supplied by the manufacturer or one specifically compatible with your battery

With correct charging and use, high-quality deep-cycle batteries are typically reliable for many years — or at least until their estimated cycle life is exceeded. 

Final Thoughts

Many factors come into play when deciding which deep-cycle battery to purchase and how to charge it.  

But it’s not as complicated as it may seem.

It’s essential to do your research using the factors outlined above to ensure the deep cycle battery you purchase is suitable for your application. 

Once you do, follow the manufacturer’s guidelines and instructions carefully. Not doing so can lead to poor performance, permanent damage, and — depending on the system — even fires or explosions. 

If you want to use a deep cycle battery for off-grid electricity storage and generation, EcoFlow offers a wide range of all-in-one solutions. 

With industry-leading LiFePO4 battery chemistry and plug-and-play operation, you can avoid many challenges of maintaining a lead acid or traditional lithium-ion deep cycle battery, optimizing its performance, and operating it safely.

Whether you need off-grid power for your next camping trip, reliable home backup power, or you’re seeking energy independence, EcoFlow has you covered. 

Check out our wide range of portable power stations and solar generators today to find your perfect fit.