Battery Warranty: Cycles, Throughput, Years & End Capacity

Short answer: A battery warranty sets multiple limits simultaneously: a number of years, a number of cycles or a cumulative MWh throughput, and a minimum remaining capacity at the end. Whichever limit is reached first ends the warranty. To compare warranties across suppliers, a buyer must understand how each parameter is measured and how the conditions attached to them affect which limit will bind.

A warranty document that lists only a cycle count or only a year figure tells an incomplete story. In practice, every serious battery warranty for cells or modules combines at least three parameters, each of which can terminate the warranty independently. Understanding the interaction between them, and the conditions that govern all of them, is the difference between a warranty that protects your project and one that expires before the asset does.

The parameters of a battery warranty

Every battery warranty is built around a set of limits. The table below maps the most common parameters, what each one measures, and what a buyer should examine closely.

Parameter	What it measures	What to scrutinise
Calendar years	Time elapsed from delivery or commissioning	Start date definition; storage periods included or excluded
Cycle count	Number of full equivalent cycles completed	Definition of one cycle; measured at cell level or pack level
Cumulative throughput (MWh)	Total energy discharged over the product's life	Measured at cell terminals or at system output; AC or DC side
End-of-warranty capacity	Minimum remaining usable capacity at warranty expiry	Measurement method; who performs the test; reference temperature
Conditions	Operational boundaries that keep the warranty valid	DoD, C-rate, temperature range, SoC during storage, BMS compliance

Whichever of the first three limits (years, cycles or throughput) is reached first, the warranty ends. End-of-warranty capacity defines what the warranty actually promises: not zero degradation, but a floor. If capacity falls below that floor before the time or energy limits are reached, it is a warranty event.

Conditions: the fine print that determines which limit you hit first

The headline cycle number means little without knowing the depth of discharge at which it was measured. Datasheet cycle life figures, including those on battery modules from Avantis Energy, are stated at 80 % depth of discharge (DoD). Cycling to a shallower depth, say 50 % DoD, generally produces more cycles before the capacity floor is reached; cycling deeper than 80 % may reduce the total number of cycles, and some warranties explicitly exclude operation beyond a stated DoD.

Other conditions that commonly appear in warranty documents:

Charge and discharge rate (C-rate): sustained high C-rates accelerate degradation; many warranties cap the continuous rate.
Operating temperature range: datasheets and warranties often give separate ranges for charging and discharging; operation outside them can void coverage.
Storage state of charge (SoC): long-term storage at full charge or near-zero charge accelerates calendar ageing; some warranties state a storage SoC range.
BMS compliance: the warranty is conditional on the battery being operated within the limits set by the battery management system. Operating outside BMS limits (overvoltage, undervoltage, overcurrent) typically voids the warranty immediately.

For prismatic LFP and NMC cells, the same principles apply at cell level, and the conditions may differ from those written into a module-level warranty.

Worked example: the same battery, two different outcomes

The following is a fictitious example constructed to illustrate the interaction of warranty limits. All figures are assumed for illustration; they do not represent any specific product or supplier commitment.

Assumed warranty terms (fictitious): - 10 calendar years from commissioning - 400 MWh cumulative throughput, which equals 4,000 full cycles at 80 % DoD on a 100 kWh system - Whichever limit is reached first ends the warranty - End-of-warranty capacity floor: 80 % of initial rated capacity

Assumed system: 100 kWh usable energy at 80 % DoD (i.e. 125 kWh nominal capacity).

Profile A, daily cycling, commercial peak-shaving: - One full cycle per day at 80 % DoD - Annual throughput: 365 cycles × 100 kWh = 36,500 kWh = 36.5 MWh per year - Years to reach 400 MWh: 400 MWh ÷ 36.5 MWh per year = 10.96 years - Binding limit: calendar years (10 years are reached before 400 MWh)

Profile B, twice-daily cycling, industrial load-shifting: - Two cycles per day at 80 % DoD - Annual throughput: 730 cycles × 100 kWh = 73,000 kWh = 73 MWh per year - Years to reach 400 MWh: 400 ÷ 73 = 5.48 years - Binding limit: throughput (400 MWh, the equivalent of 4,000 full cycles, is reached in approximately 5.5 years)

The system is identical. The warranty expires at year 10 for a once-daily user and at roughly year 5.5 for a twice-daily user. A buyer specifying a system for Profile B who negotiates only on calendar years will be disappointed. The correct negotiating lever is cycle count or MWh throughput, whichever reflects the intended use. Also check how cycles are counted. A throughput limit uses up energy in proportion to what is discharged, so partial cycles consume it slowly. A cycle counter that registers every partial cycle as a full cycle would use up a cycle limit faster than a throughput limit. Ask which definition the warranty uses.

For guidance on how cycle assumptions feed into a project business case, the article When is C&I energy storage cost-effective? works through the underlying economics.

End-of-warranty capacity: what the floor actually means

A warranty that promises 80 % remaining capacity after 4,000 cycles does not mean the battery will degrade to exactly 80 % and stop. It means: if capacity falls below 80 % of the original rated value before the throughput or year limit is reached, the buyer has a warranty claim.

What to establish before signing:

Measurement method: remaining capacity must be measured under defined conditions: temperature, C-rate and SoC range. A capacity test at 25 °C and 0.2C gives a different result from a field measurement at 5 °C and 1C.
Who supplies the data: in most deployments, the buyer's BMS or EMS holds the cycle counter and the capacity estimates. Clarify whether the warranty claim process requires third-party testing, manufacturer-supplied test equipment, or data exported from the BMS.
Who performs the test: some warranties require the manufacturer or an approved laboratory to perform the reference capacity test. Others accept BMS-logged data. The difference matters when you are filing a claim.
Reference capacity: is the floor calculated against the nameplate capacity or the measured initial capacity at commissioning? If the delivered capacity was 98 % of nameplate, an 80 % floor calculated against nameplate gives a different threshold than 80 % of the measured value.

IEC 62619, the international standard for secondary lithium cells and batteries for use in industrial applications (published by the International Electrotechnical Commission), sets out safety requirements but does not prescribe warranty terms. The EU Battery Regulation 2023/1542 (EUR-Lex, europa.eu) introduces requirements on performance, durability and state-of-health information for certain battery categories, phased in over time, which will increasingly shape what suppliers are required to document and disclose. Buyers specifying systems for European markets should track which product categories fall under those obligations; our article on the regulation gives an overview.

What to get in writing before purchase

A technically complete warranty section in a supply agreement should state:

All three time/energy limits and the method for determining which is reached first
The capacity floor and the exact measurement protocol
The complete list of operating conditions (DoD, C-rate, temperature, storage SoC, BMS compliance)
The data source for cycle counting and throughput tracking
The claim procedure: notice period, required evidence, response time and remedy (repair, replacement, or prorated credit)
Whether the warranty is transferable if the system changes hands; relevant for energy storage solutions that may be resold or repurposed

For complete module systems, the warranty scope may sit at the module level, the cell level, or both, and the two may carry different terms. Establish which entity is the warrantor for each layer. The RFQ checklist for battery modules shows where warranty requirements belong in an enquiry.

Frequently asked questions

What does battery warranty throughput in MWh actually measure?
Cumulative MWh throughput is the total energy discharged from the battery over its lifetime, measured at a defined point, typically the cell or module terminals. It is an alternative to cycle count: a battery cycled at partial depth accumulates MWh more slowly than one cycled to full depth, so throughput captures actual usage regardless of cycle depth.

Why do battery warranties specify cycle life at 80 % depth of discharge?
Cycle life figures on datasheets are measured at a standardised depth of discharge, most commonly 80 % DoD. Cycling to a shallower depth typically yields more cycles before the capacity floor is reached; cycling deeper than 80 % may reduce total cycle life. Using the 80 % DoD figure as a sizing basis is the standard practice; applying it to a different operating profile requires adjustment.

Which warranty limit (years, cycles or MWh) is most likely to bind in a stationary storage application?
It depends on the cycling frequency and on the terms. In the worked example above, a system cycled once daily at 80 % DoD reaches the calendar limit first, and a system cycled twice daily reaches the throughput limit after about five and a half years. Calculate every limit against your intended use profile before negotiating terms.

What should a buyer verify about the end-of-warranty capacity measurement?
Establish the reference temperature and C-rate for the capacity test, who performs it (manufacturer, independent laboratory, or BMS data), whether the floor is calculated against nameplate or measured initial capacity, and what constitutes acceptable evidence for a warranty claim. These details determine whether a claim is straightforward or disputed.

Does operating outside the BMS limits void a battery warranty?
In most warranty documents, yes. Operation outside the boundaries set by the battery management system (overvoltage, undervoltage, overcurrent or temperature exceedance) is typically listed as an exclusion that invalidates the warranty, regardless of the remaining cycle count or calendar time. Confirm the exact exclusions in the warranty text before commissioning.

Discuss your specification with Avantis Energy

Bringing a defined use profile (cycles per day, DoD, temperature range and system lifetime) to a pre-purchase conversation allows both parties to match warranty terms to actual operating conditions. Contact Avantis Energy to discuss your project requirements.