Lithium Battery Warranties and What You Should Know
Lithium batteries are one of the most expensive and critical components of a home solar power system. Whether you’re off-grid or grid-connected with hybrid capability, understanding the warranty terms of your battery is essential to ensuring you get the performance and lifespan you expect. Unfortunately, most battery warranties include fine print and usage conditions that are often misunderstood or overlooked. These can impact your eligibility for a warranty replacement, even if the battery is still technically within the advertised warranty period.
This article will explain the key parts of lithium battery warranties you need to know, including end-of-life capacity (EOL) and minimum energy throughput limits. Plus, we explain the impact of overnight grid charging and how you can adjust system settings as your battery ages.
Battery Degradation Explained
All lithium-ion batteries degrade over time — this is an inherent chemical process that occurs with each charge and discharge cycle. Even with careful use and ideal conditions, the battery’s ability to store and deliver energy gradually decreases. Typical degradation rates vary depending on battery chemistry, temperature, usage patterns, and management systems. However, most high-quality lithium batteries (especially LFP-based systems) degrade at an average of:
2% to 3% capacity loss per year, in a well-designed and moderately used system.
Some batteries may degrade 1.5% per year or less under light use or shallow cycling.
This natural loss of capacity is factored into the warranty, which is why manufacturers specify the minimum capacity at the end of the term, known as the End-of-Life (EOF). However, even if the battery has reached the end-of-life capacity as stated in the warranty, it does not mean the battery can no longer be used. As long as the battery is functional and operating without errors, technically, it can be used for many more years. Learn how you can increase the life of your lithium battery.
Key Warranty Metrics
When evaluating or comparing lithium batteries for a solar storage system, it’s essential to go beyond the marketing brochures and look at the actual warranty document. While many manufacturers advertise “10-year warranties,” the real limitations and coverage are defined by two key metrics:
End-of-Life (EOL) Capacity – the minimum guaranteed usable capacity after a certain number of years or cycles
Energy Throughput – the maximum amount of energy (in MWh) the battery can deliver before the warranty expires, regardless of time
These two values are the foundation of most lithium battery warranties, and they often work on a "whichever comes first" basis. That is, the battery is warranted for 10 years or 30MWh, whichever limit is reached first.
Battery End-of-Life Capacity
One of the most important and often misunderstood aspects of any lithium battery warranty is the End-of-Life (EOL) capacity guarantee. This defines the minimum amount of usable energy the battery is expected to provide at the end of the warranty period (typically 10 years). Nearly all battery warranties state this value as a percentage of the original (nominal) capacity, usually between 60% and 80%, depending on the manufacturer.
For example:
A 10kWh battery with a 70% EOL guarantee means the battery should still deliver at least 7kWh of usable energy after 10 years of use, provided you haven’t exceeded the warranty’s cycle or throughput limits.
When sizing a solar battery system, it’s important to remember that:
Your 10kWh battery will not always give you 10kWh over its lifespan.
After 8–10 years, you may only get 6–8kWh of usable energy per cycle
If you need a certain amount of backup energy (e.g., for off-grid use), you should oversize your battery bank upfront to account for future capacity fade.
🔍 Important: If your battery falls below the stated EOL capacity before the warranty period ends (and you haven’t exceeded the energy throughput or cycle limits), this should qualify as a warranty claim.
2. Battery Minimum Throughput
Throughput refers to the total amount of energy (in kilowatt-hours or megawatt-hours) the battery is allowed to cycle before the warranty expires, regardless of time. If you use your battery heavily and charge it overnight and well as during the day (double charge cycle), the throughput limit may be hit before the 10-year mark. Throughput is often the true limiting factor in real-world use. As explained below, you can calculate the warranty time period against the total energy throughput when evaluating warranties.
How to Calculate Minimum Throughput
Minimum throughput is the total energy the battery is guaranteed to provide over its usable life. It’s a more accurate measure of battery wear than time alone, especially in systems with high usage.
Battery Capacity (kWh) × Cycle Count × Depth of Discharge (DOD%) = Throughput (kWh)
For example:
10kWh battery
1 full cycle per day (at 80% DOD) = 8kWh
365 days × 10 years = 3650 total cycles
8kWh x 3650 = 29.2MWh of total energy throughput
However, if your warranty only covers 30MWh, you would exceed this if you discharged your battery deeper than 80% DOD, regardless of whether the 10-year period has passed.
✅ Pro Tip: Some inverters and battery monitors (like Victron SmartShunt and Selectronic inverters) track cumulative energy throughput, making it easier to compare actual usage against the warranty limit.
Issues with Overnight or Off-peak Battery Charging
Many hybrid inverters now allow scheduled charging of your battery from the grid during off-peak periods, which is especially useful in winter or poor weather when solar production is limited.
Here’s how it works:
During the day, the battery charges from solar and discharges in the evening.
At night (often after midnight), it recharges using off-peak grid energy.
The battery then discharges again in the early morning, effectively doubling the daily throughput.
This strategy can be financially beneficial, especially in areas with time-of-use tariffs, but it can dramatically increase the cumulative energy throughput of the battery. If done throughout the year, this can double your total energy throughput, causing you to hit the warranty limit years earlier than expected. The battery usage pattern should be managed with the warranty conditions in mind.
Warranty Conditions - The Fine Print
Beyond the key metrics, such as 10 years, 6000 cycles, or 70% end-of-life capacity, every lithium battery warranty contains a list of operating conditions and exclusions that can invalidate a claim if not followed. These details are often buried in the full warranty document or installation manual and are not mentioned in the sales brochure or data sheet.
These conditions typically cover things like temperature limits, charge/discharge rates, required maintenance, compatible equipment, and data logging. In some cases, failing to meet a single condition — even inadvertently — could allow the manufacturer to deny a warranty replacement, even if the battery has degraded or failed. However, consumer laws in some countries may enable you to claim a warranty even if a condition was not met due to it being unrealistic in real-world use.
📄 Example Warranty Extract:
Here’s a typical excerpt from a lithium battery warranty document:
"Cycle Definition: A cycle is defined as a complete 100% charge and 100% discharge. Partial cycles are aggregated to determine equivalent full cycles."
"Conditions: This warranty is valid only if the battery is operated within its specified temperature range, charged to 100% SOC at least once every 30 days, and used with a compatible inverter or BMS. The system must have data logging enabled, and warranty claims must include performance logs showing voltage, SOC, and temperature data."
Full Charge Requirements
Many warranties stipulate the battery must be charged to 100% SOC (State of Charge) at least once every 7 to 14 days to allow for cell balancing. Cell balancing helps maintain long-term battery health and accuracy of the SOC reading. Additionally, the battery charge voltage (absorption) settings may be critical to ensuring the battery cells are balanced correctly.
🌡️ Operating Temperature Range
All lithium battery warranties specify an allowable temperature range.
Typical range: 0°C to 45°C (charging), and -10°C to 55°C (discharging)
Exceeding these limits, even briefly, may void the warranty, especially for indoor-rated batteries used in uninsulated garages or sheds.
❄️ Tip: Some batteries allow limited charging below 0°C using preheating functions, but these must be enabled in the inverter/BMS. If you're in a cold climate, make sure your system is set up correctly for winter.
Data Logging Requirements
Many manufacturers require performance data for warranty claims, especially for self-managed systems. If the battery monitor or BMS doesn’t record SOC, voltage, throughput, and error codes, your claim may be denied due to a lack of evidence.
Adjusting System Settings to Account for Capacity Loss
As your battery ages and its capacity begins to fade, you may need to adjust your system settings to match its real-world performance and account for the capacity fade over time. If you do not account for the loss, especially with certain types of self-managed lithium batteries such as those used for off-grid systems, the low-voltage battery cutout setting may be reached, causing your system to shut down unexpectedly, resulting in a blackout. If this occurs regularly, you risk accelerating the battery degradation due to additional stress put on the battery.
Self-Managed Batteries (e.g. PowerPlus, GenZ, Rixiu)
These systems rely on the inverter or chargers to manage operation and track the state of charge and battery capacity. They do not report internal battery State of Health (SOH), so the user or system installer should make manual adjustments every few years to account for capacity fade:
Update Capacity Settings: Reduce the Ah or kWh value in your inverter to reflect the current usable capacity.
Adjust SOC Cutoff Limits: Raise the minimum SOC to avoid over-discharging as usable capacity decreases.
Monitor Throughput: Use Victron SmartShunt (“Cumulative Ah drawn”, “Energy in kWh”) or Selectronic log data to track lifetime energy use.
If capacity has reduced significantly (e.g., from 10kWh to 7kWh), your system will underperform and could even shutdown unless the inverter parameters are updated accordingly.
Managed Batteries (e.g. Pylontech, BYD, EG4)
These batteries use more advanced Battery Management Systems (BMS) and communicate with the inverter, and control the charging and discharging parameters, taking into account capacity fade.
The system automatically adjusts based on the internal State of Health (SOH)
Still important to monitor performance data and maintain firmware updates
Note: Some systems like EG4 and some Chinese LFP models (e.g., Rixiu) are increasingly offering hybrid features — sometimes blurring the line between self-managed and fully managed systems. Be sure you inverter is configured to take into account the battery SOH and ensure the battery low-voltage cut-out settings are correct.
Summary – What You Need to Know
Understanding lithium battery warranties is essential for anyone investing in a solar or off-grid power system. While many battery manufacturers advertise a 10-year warranty, this coverage is almost always conditional and typically ends once a certain energy throughput or cycle count has been exceeded, whichever comes first. For homeowners with high daily energy usage, or those enabling overnight/off-peak charging throughout winter, it’s quite possible to exceed the warranted energy throughput long before the 10-year term has elapsed. This highlights the importance of knowing both how your system operates and how warranty conditions are structured.
In addition to performance metrics, most warranties include specific operational requirements that users must follow to remain eligible for coverage. These often involve maintaining operation within a prescribed temperature range, ensuring the battery is fully charged to 100% on a weekly basis (to enable internal cell balancing), and using only compatible or approved inverter systems. These conditions are sometimes buried deep within the fine print and are easily overlooked, but they can be grounds for a denied warranty claim.
In summary, a lithium battery warranty is not just a fixed timeframe; it’s a performance-based promise that depends on how the battery is used, maintained, and monitored. Being aware of key metrics like total energy throughput and operational conditions is essential to ensure you remain compliant and get the maximum return on your investment. For installers and homeowners alike, reading and understanding the full warranty document is the best way to avoid surprises down the road.
Learn how you can increase the life of your lithium battery.
