Cell Diagnostics & Testing

Second-Life Grading at 75–85% Capacity

Q: Why is 75-85% SOH the second-life window for EV batteries?

Below 80% SOH a pack no longer meets automotive range and power expectations, but stationary storage runs at much lower C-rates and tolerates reduced capacity. Modules entering stationary duty at 75–85% SOH typically deliver another 2,000–2,500 cycles before reaching a 60% end-of-service threshold.

Q: How many more years can a repurposed EV battery last?

In daily-cycled stationary duty, a module repurposed at 80% SOH commonly lasts 7–10 further years. Lower-cycle applications such as backup power extend that further, and LFP modules outlast NMC in the same duty.

Q: Can a grade C module ever be used in storage?

Sometimes, in low-duty backup with conservative limits and a short warranty. Most grade C modules are better used for cell harvesting.

Q: Does grade depend on chemistry?

The SOH bands are the same, but chemistry affects expected remaining life, so warranty terms and suitable applications differ between LFP and nickel-rich modules.

Q: How is a grade challenged if a buyer disagrees?

The signed test record for the module can be reviewed, and a retest under the same conditions can be arranged.

The 75–85% SOH window is where an automotive-retired module becomes a stationary storage asset. Our grading protocol turns that window into consistent, binned, warrantable product.

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Second-life conversion

42%

Of all intake modules

Capacity bin width

2.5%

Within a string set

Further cycles typical

2,400

Stationary duty to 60% SOH

Warranty claims

0.6%

Of modules shipped

Overview

The short version

Second-life grading turns a mixed stream of retired modules into products with predictable behaviour. Without a consistent protocol, used modules are hard to price, hard to warrant and hard to integrate. With one, they become a supply that storage developers can design around and financiers can underwrite.

Our protocol combines capacity, resistance, impedance, balance and self-discharge into one grade, then groups modules into narrow bins. The grade decides where a module can go; the bin decides which other modules it can be paired with. Both are recorded against the module serial so the decision can be checked later.

Capabilities

What this programme includes

Grade A — BESS ready

Above 85% SOH, tight balance, no EIS anomalies. Direct to string build.

Grade B — second life

75–85% SOH. Binned and impedance-matched for commercial storage duty.

Grade C — harvest

65–75% SOH. Healthy cells harvested; remainder to refining.

Grade D — recycle

Below 65% or any safety flag. Straight to hydrometallurgy.

String set assembly

Modules issued as matched sets with a combined performance certificate.

Capacity-backed warranty

5-year warranty underwritten against the graded capacity figure.

Workflow

How engagement runs

1
Measure
SOH cycling and EIS combined into a single grade vector.
2
Bin
Modules sorted into 2.5% capacity and resistance bands.
3
Match
String sets composed from a single bin with matched impedance.
4
Certify
Set-level datasheet and warranty certificate issued.

Specification

At a glance

Parameter	Detail
Grade A threshold	> 85% SOH
Grade B window	75 – 85% SOH
Balance limit	< 50 mV cell spread
Self-discharge limit	< 3 mV / 24 h
Standard	UL 1974 evaluated

Second-Life Grading at 75–85% Capacity — technical specification.

From grade to application

Each grade has a clear destination. Grade A modules, at 85% SOH and above with clean diagnostics, go into grid-tied or commercial storage where they will cycle regularly. Grade B modules, between 75% and 85%, suit telecom backup and solar buffering. Grade C modules, between 65% and 75%, are used for cell harvesting or low-duty backup with shorter warranties.

Grade D covers anything below 65% or with any safety concern. Those modules are discharged and sent for refining, because the risk and the limited remaining capacity outweigh any reuse value.

Grade	Measured SOH	Typical destination
A	85% and above	Grid-tied and commercial storage
B	75–85%	Telecom backup, solar buffering
C	65–75%	Cell harvest, low-duty backup
D	Below 65% or safety flag	Discharge and refining

Grade bands and typical destinations.

Why binning and matching matter

Modules in a series string share the same current, so the weakest one sets the limit for the whole string. If capacity and resistance vary widely, the string loses usable energy and the weakest module is overstressed, which accelerates its decline. Tight bins keep modules working within the same envelope.

Matched sets also simplify balancing. The battery management system spends less energy correcting imbalances, and the string reaches end of life more evenly, which makes warranty terms easier to set and honour.

Group by capacity and by resistance, not capacity alone
Keep chemistry and format consistent within a string
Record bin data per module for warranty tracking
Retest stored modules before dispatch

Field note

Modules held in stock should be stored below 30% state of charge and retested before they are shipped.

Answers

Technical FAQ

Why is 75-85% SOH the second-life window for EV batteries?

Below 80% SOH a pack no longer meets automotive range and power expectations, but stationary storage runs at much lower C-rates and tolerates reduced capacity. Modules entering stationary duty at 75–85% SOH typically deliver another 2,000–2,500 cycles before reaching a 60% end-of-service threshold.

How many more years can a repurposed EV battery last?

In daily-cycled stationary duty, a module repurposed at 80% SOH commonly lasts 7–10 further years. Lower-cycle applications such as backup power extend that further, and LFP modules outlast NMC in the same duty.

Can a grade C module ever be used in storage?

Sometimes, in low-duty backup with conservative limits and a short warranty. Most grade C modules are better used for cell harvesting.

Does grade depend on chemistry?

The SOH bands are the same, but chemistry affects expected remaining life, so warranty terms and suitable applications differ between LFP and nickel-rich modules.

How is a grade challenged if a buyer disagrees?