Practical Battery Knowledge: Charging, Discharging & Real-World Realities

When it comes to batteries, there's a big difference between lab results and what really happens out in the field. At Element 82, we see firsthand how batteries perform under load, in the weather, and through the seasons. This article expands on our earlier insights and digs deeper into charging conditions, generator use, DC charging, and the limitations imposed by both physics and modern Battery Management Systems (BMS). Whether you're off-grid, on the water, or just want a system that works, here’s what you need to know.

Usable Capacity and Depth of Discharge (DoD)

Batteries are rated for a theoretical 100% depth of discharge, but that’s rarely how they’re used—or should be.

• Lithium Batteries: Technically capable of 100% DoD, but in practice, most BMS systems restrict use of the top ~10% and bottom ~10% of capacity to preserve cell health. What you actually get is around 60–80% usable capacity.

• AGM Batteries: While they can be discharged fully, this drastically shortens lifespan. Most users will get better results cycling between 50–80% DoD.

Charging Conditions Matter

Charging is not a one-size-fits-all situation, and how (and when) you charge your battery makes all the difference.

• Lithium: Quick to recharge, but temperature-sensitive. Most lithium chemistries can’t accept a charge below 0°C. If charging continues below freezing, lithium plating can occur, permanently reducing capacity. A quality BMS will cut charging to prevent this, but it also means you might be without power until the battery warms up.

• AGM: More tolerant of cold, and although charging takes longer, it doesn’t require BMS protections. AGM batteries will accept a charge at colder temperatures and are more forgiving to mismatched chargers, though temperature compensation is still important.

Generator & DC Charging Considerations

Generators paired with lithium batteries can be tricky. Lithium wants high current until it’s full, then no current. But many generators don’t respond well to this sudden drop in demand and may surge or stall. You’ll need a smart charger or DC-DC converter that buffers this.

For vehicles, DC charging (from alternators) is common. However:

• Smart Alternators: These often drop voltage to save fuel, meaning lithium batteries won’t charge unless you install a DC-DC charger.

• AGM Batteries: More adaptable to alternator voltage swings, and many older vehicles can charge AGMs directly.

Charger Sizing and Timed Stages

Battery chargers often use timed stages. If your charger is too small (like 5A for a 150Ah battery), it may never reach the thresholds required for switching stages within the time limit, triggering an error or incomplete charge. Ideally:

• Use a charger rated to at least 5–10% of your battery’s Ah rating (e.g., 15A for a 150Ah battery).

• For maintenance charging, 1/20th of capacity can suffice—but only if the battery is already full.

Charging slowly also has the benefit of reducing heat buildup, which can extend battery life for both AGM and lithium chemistries.

Standards and Specifications: What Really Matters

Too much focus is placed on headline specs without considering the test conditions or limitations:

• CCA, MCA, HCA Ratings: These cranking numbers are important but are all based on different temperatures. Make sure you're comparing like for like.

• Reserve Capacity (RC): Often overlooked, RC is crucial for applications like RVs, boats or off-grid homes. It represents the time a battery can deliver a constant load before voltage drops below a usable level.

• BMS Limitations: Many warranties only allow one full cycle per day—something internet forums rarely mention. Some BMS units also throttle performance in high heat or freezing temps to protect the cells.

Myth Busting: Online Hype vs. Reality

• 100% DoD daily? Sure, in theory. But your warranty likely disagrees.

• Fast charge any time? Only if heat and BMS cutouts aren’t a concern.

• Plug-and-play lithium swap? Only if your entire system was designed for it.

• Temperature compensation is standard? Not always. Many chargers don’t truly adjust charge voltage based on ambient temperature unless paired with an external sensor.

Real-world performance depends on wiring, charger specs, climate, and user habits—none of which get factored into those glossy marketing brochures.

Final Thoughts: There’s No Perfect Battery

Whether it’s AGM, lithium, gel, or something else—every battery chemistry has trade-offs. The right choice comes down to:

• Your application

• Your environment

• Your budget

• Your ability to manage the system

AGM offers simplicity and robustness. Lithium offers performance and energy density—but only when supported by the right infrastructure.

At Element 82, we look at the whole system—not just the battery—because no component works in isolation. Understanding the limitations and capabilities of each technology is key to designing a reliable and safe power system.

Need the Right Advice? Talk to us at Element82.co.nz. We’re here to match real-world problems with real-world solutions, not just hype.

As proud members of SEANZ (Sustainable Energy Association of New Zealand), we have established ourselves as a trusted and reliable solar provider in the industry. Our commitment to promoting sustainable energy solutions aligns perfectly with SEANZ's mission of fostering a clean and renewable future for New Zealand. With a deep understanding of the latest solar technologies and industry best practices, we strive to deliver top-quality solar installations, exceptional customer service, and long-term energy solutions that meet the unique needs of our clients. Our SEANZ membership serves as a testament to our dedication to excellence, adherence to ethical business practices, and our ongoing efforts to contribute to a greener and more sustainable New Zealand.

Understanding Battery Technologies: Cutting Through the Hype

When it comes to batteries in real-world applications, there’s a lot of information out there—and not all of it is helpful. At Element 82, we believe in presenting honest, practical advice based on how batteries perform in actual use cases, not just on spec sheets or internet chatter. This article unpacks the realities of charging and discharging batteries, explores different battery technologies, and debunks some common myths floating around online.

Rated Capacity vs. Usable Energy

Every battery is marketed with a certain capacity, often stated in amp-hours (Ah) or kilowatt-hours (kWh). But what does this actually mean in practice? For most battery types, including lithium and AGM, the full stated capacity isn't always usable.

• Lithium Batteries: Even though they're often promoted as allowing 100% depth of discharge (DoD), in practice, the usable range is closer to 80%. The Battery Management System (BMS) limits the top and bottom end of the charge range to protect the cells, meaning you typically get about 70-80% of the rated capacity in real-world cycling.

• AGM Batteries: These also don’t deliver full capacity unless discharged completely, which isn’t advised due to drastically reduced cycle life. Typically, AGM batteries are best cycled between 50% and 80% DoD to preserve lifespan. This info may be right for a motorhome with light weekend use once a month as you'll still enjoy many years of weekend use. But if you lived off-grid anyone with 10 years of experience living that way will tell you that only discharging to 70% state of charge (30% discharged) will give you over 2500 cycles or almost 7 years of usable life cycles and if you don't discharge daily that will further extend your batteries expected life years.

Charging Considerations: Rate, Temperature, and Compatibility

A battery is only as good as its charging regime. Overcharging, undercharging, or using an incompatible charger can all result in poor performance or outright failure.

• Lithium: Fast charging is possible and often promoted, but comes with the trade-off of increased heat and potential wear on the cells. Charging in temperatures below 0°C is a big no-go, as lithium cells can be permanently damaged. A good BMS will prevent charging below freezing, but in cold climates, you may need a battery with an integrated heater or external heating mat.

• AGM: Slower to recharge and less efficient, but far more forgiving. AGMs can handle a range of charge voltages and don’t require temperature control to the same extent. However, temperature compensation is still recommended to avoid undercharging in cold weather or overcharging in hot weather.

Notably, the CTEK MXS 5.0 charger does not truly offer temperature compensation despite what many forums claim. It derates based on internal temperature to protect itself, not to optimise charging voltage based on ambient temperature. For accurate temp compensation, use a charger with a dedicated external sensor.

Environmental Impacts

• Solar Panel Orientation: In colder, southern climates like New Zealand’s South Island, the sun sits lower in the sky during winter. This means solar panels should be mounted at steeper angles to capture more sunlight and produce usable energy when it's needed most.

• Battery Performance: Cold weather severely impacts lithium batteries more than AGM as Lithium should never be charged below zero degrees C, Lead Acid shouldn't be charged below minus 20 degrees C as the battery will freeze (due to its water content). Heat management is also critical for both chemistries (lead acid charging generates thermal activity) to avoid reduced performance or BMS lock  outs due to sub-optimal charging or discharging temperatures.

Application vs. Internet Hype

Online forums and marketing material often highlight the best-case scenarios: 100% DoD, ultra-fast charging, or thousands of cycles. But these claims rarely hold up under real-world conditions.

• Overstated Claims: Internet sources often ignore critical limitations like BMS protections, charge rate limitations due to heat, or warranty clauses that only allow one full cycle per day.

• System Compatibility: Swapping from AGM to lithium isn’t just a plug-and-play upgrade. It may require a new charging system, BMS integration, and possibly safety standards approval and considerations.

Why AGM Still Has a Place

Despite the lithium hype, AGM batteries remain relevant in many systems. They are robust, simple, and require minimal active management. For legacy systems or where reliability outweighs peak performance, AGM is still a smart choice.

Conclusion: Choosing the Right Battery For Your Needs

There's no one-size-fits-all battery. Your choice should depend on your application, budget, climate, and performance expectations. Lithium offers impressive specs but demands precise management and often additional infrastructure. AGM remains a steady, dependable option.

At Element 82, we help customers find the right solution, not just the trendiest one. Whether you're powering an RV, marine vessel, off-grid home, or industrial site, we focus on performance that works in the real world—not just on paper.

Need Help With Battery Selection? Reach out to us at Element82.co.nz for advice tailored to your setup, climate, and energy goals.

Leading the Way in Mobile, Intelligent, and Renewable Power Solutions

At Element 82, we're committed to delivering top-notch power solutions that meet your every need. Our internationally manufactured products are locally supplied, ensuring you get the best of both worlds - cutting-edge technology and fast delivery. We're proud to import and distribute some of the world's leading DC power brands, including CTEK, Odyssey, Alfatronix, and more. With certifications from the car industry, telecommunication, emergency services, aviation, and more, our products are built to deliver reliable and efficient power for any application. Whether you need off-grid or grid-tied systems, Element 82 has the solution for you.

Don't settle for mediocre power solutions. Upgrade to the best with Element 82. Contact us today to see how we can transform your power experience.