How to Read Battery Health SOH? Li-ion / Na-ion Attenuation Assessment and Replacement Timing + AI Smart Status Assessment APP

I. What Is SOH: Definition and Three Assessment Methods

SOH represents the remaining health of a battery as the ratio of its "current actual usable capacity" to its "factory-rated nominal capacity." It differs from SOC: SOC answers "how much charge is left right now," while SOH answers "how much of this battery's life has been used up." A battery showing 80% SOC could have an SOH of 95% or just 72%—the two carry entirely different maintenance implications.

In engineering practice there are three common SOH assessment methods. Typically a fast method is used for initial screening, then a slow method is used for confirmation.

Assessment Method	Procedure	Required Conditions	Characteristics & Use
Capacity calibration	Discharge at constant current to the cut-off voltage, integrate the released charge, and compare against nominal capacity	Requires the whole battery to be fully dischargeable, taking several hours	Highest accuracy; the final basis for replacement decisions
Internal resistance & voltage-difference	Measure resistance growth; observe per-cell / per-branch charge-discharge voltage differences within the pack	Can be read quickly during charging or at rest	Fast, online; suitable for daily inspection and early warning
Charge-discharge curve	Compare the plateau position of the voltage-capacity curve, the inflection point, and the plateau voltage	Collected in a single charge-discharge cycle	Between the two above; shows trends but should not be used alone for a definitive verdict

The usual practice is: monitor trends daily with internal resistance and voltage-difference; once attenuation is suspected, arrange a full constant-current discharge calibration to confirm.

II. Attenuation Characteristics Across Battery Chemistries

Battery Chemistry	Main Source of SOH Attenuation	Reading Tips	Replacement Threshold Notes
LiFePO₄ (LFP)	Long-term float charging, prolonged high-SOC dwell, high-temperature calendar aging	Capacity fades gently but high temperature accelerates it; per-cell voltage difference is an early signal	Enter replacement evaluation when voltage difference keeps growing or SOH drops below 70%
Sodium-ion (Na-ion)	Primarily cycle consumption; rate and temperature effects are more pronounced	Under low-rate operation, cycle-life data outperforms lithium; specific conditions are as stated on the product page	Torchn sodium battery product page states a cycle life of 8000 cycles (0.5C, 90% DOD, 25±2℃); this figure is a cycle-test result under specific conditions and does not equal SOH under arbitrary usage
Gel lead-acid	High float voltage, plate sulfation, water loss	Capacity declines markedly with high temperature and long-term shallow charge/discharge use	Judge by capacity calibration and float current, not voltage alone

Though all are "energy storage batteries," lithium ages more on the time axis (calendar aging), sodium more on the cycle axis, and gel lead-acid shows both. The three cannot share one SOH threshold.

III. SOH Grading, Maintenance, and Replacement Decision Table

The table below shows common experience-based grading. In actual execution, also combine load ratio, ambient temperature, and manufacturer recommendations—specifics are as stated on the official product page and manufacturer technical documents.

SOH Range	Status Reading	Maintenance Action	Replacement Advice
> 90%	Capacity essentially ample, in healthy period	Keep routine inspection, record capacity baseline	No replacement for now
80%–90%	Mild attenuation, usable capacity slightly reduced	Recheck intra-pack per-cell voltage difference and charge-discharge temperature; build a capacity-trend record	No replacement for now; add to watch list
70%–80%	Moderate attenuation, endurance and load margin clearly down	Arrange a constant-current discharge calibration to confirm; adjust depth of discharge and charge temperature	Plan replacement; timing depends on backup-power needs
< 70%	Severe attenuation, near end-of-life boundary	Reduce load and discharge depth; avoid prolonged high-current discharge	Replacement recommended; also recheck inverter-to-battery compatibility

IV. How to Measure SOH: Constant-Current Discharge Calibration Steps

Constant-current discharge calibration is the only method that yields a reliable SOH value. The core is "discharge the battery empty once at a fixed current, then integrate the released charge back."

1. Preparation: Confirm the battery is fully charged (float stage ended or just finished charging); record ambient temperature, discharge load, and cut-off voltage. For large-capacity cabinets, use a stepwise unloading via adjustable electronic load first to avoid a one-shot high-current shock.

2. Set constant-current discharge: Start at about 0.2C of rated capacity—e.g., a 51.2V 200Ah rack battery can first discharge at roughly 40A constant current; too high a current makes voltage drop prematurely and read low.

3. Record throughout: Every 5–10 minutes record voltage, current, and cumulative ampere-hours released, until voltage hits the cut-off threshold (an LFP system usually stops when the cell approaches minimum discharge voltage; the exact threshold is as per the product and inverter settings).

4. Integrate for capacity: Sum the ampere-hour segments to get measured capacity, then compare with nominal capacity for SOH.

5. Observe consistency simultaneously: When branches discharge in parallel in the same pack, compare each branch's voltage and ampere-hour deviation; an obvious voltage difference means intra-pack consistency has dropped.

6. Recharge and record: After calibration, recharge per the manufacturer procedure and fully charge again, as the baseline for the next calibration.

Calibration consumes one full cycle and accelerates aging, so it need not be done frequently—quarterly or aligned with the maintenance plan is recommended.

V. Formulas and Calculation Examples

Formulas:

Example 1 (by nominal capacity): Take the Torchn WKC F02-51.2200 rack-mounted storage lithium battery (51.2V 200Ah, 10.24kWh, id=46). Calibration releases 176.0Ah measured, so SOH = 176.0 ÷ 200 × 100% = 88.0%, landing in the 80%–90% band—recommended to build a capacity-trend record and recheck intra-pack voltage difference, no replacement for now; usable energy by nominal voltage = 176.0 × 51.2 ÷ 1000 ≈ 9.01kWh.

Example 2 (near replacement threshold): The same id=46 battery, calibrated again one year later, releases 138.0Ah measured, SOH = 138.0 ÷ 200 × 100% = 69.0%, already below 70%—shrink discharge depth, avoid prolonged high-current discharge, and enter the replacement evaluation process.

VI. Reference Models (Real Parameters, as Stated on the Official Product Page)

Model	Category	Product Page ID	Key Parameters	Link
Torchn WKC F02-51.2200	Rack-mounted storage lithium battery	46	51.2V 200Ah, 10.24kWh, 83Kg, 530×720×140mm, fits inside 19-inch cabinet, parallel up to 20 units, UN38.3 / MSDS / CE	https://www.torchn.com/productDetail.html?id=46
Torchn WKC F02-51.2100	Rack-mounted storage lithium battery	45	51.2V 100Ah, 5.12kWh, 42.7Kg, 440×550×140mm, parallel up to 20 units, UN38.3 / MSDS / CE	https://www.torchn.com/productDetail.html?id=45
Torchn WKC F01-51.2100	Wall-mounted residential storage lithium battery	20	51.2V 100Ah, 5.12kWh, 43.2Kg, 380×148×615mm, parallel up to 20 units, UN38.3 / MSDS / CE	https://www.torchn.com/productDetail.html?id=20
Torchn WKC FNa01-4850	Wall-mounted residential storage sodium battery	64	48.45V 50Ah, 2.422kWh, 42.5Kg, 380×148×615mm, cycle life 8000 cycles (0.5C, 90% DOD, 25±2℃), parallel up to 20 units, UN38.3 / MSDS / CE	https://www.torchn.com/productDetail.html?id=64

Taking the verified WKC F02-51.2200 (id=46) as an example: rated voltage 51.2V, rated capacity 200Ah, stored energy 10.24kWh, using large-capacity Grade-A LiFePO₄ cells, with the product page stating a service life of 15+ years; rack-mount design fits inside a 19-inch cabinet; has Bluetooth function for real-time battery status monitoring; built-in intelligent protection covering over-voltage, under-voltage, voltage-difference, over-temperature, capacity, short-circuit, and communication-failure protections; protocol library covers 95%+ of mainstream off-grid storage inverters on the market, applied to telecom backup power and home energy storage. The same series also includes a 51.2V 200Ah slim version (10.24kWh, id=22) and a wall-mounted 51.2V 100Ah (id=20); the official product page does not specify cycle counts for every model—service life and cell grade are as stated on the official product page.

Smart Management APP (Bluetooth / WiFi + AI Active O&M)

Without opening the cabinet for calibration, continuous health tracking is impossible. The self-developed smart management APP by Yangzhou Dongtai Power Supply connects and manages inverters, lithium batteries, and sodium batteries via a Bluetooth or WiFi module—Torchn's rack lithium (id=46) and wall-mounted sodium (id=64) product pages both state a Bluetooth function for real-time battery status monitoring.

The APP embeds AI that continuously analyzes device working status and user habits, delivering neutral, objective status assessments and usage suggestions: for instance, judging capacity-attenuation trends from long-term charge-discharge records, flagging an expanding intra-pack voltage difference, and suggesting reduced float duration in hot seasons. The role of AI is to turn "calibration" from a one-off action into continuous observation—when the system detects sustained capacity decline or abnormal voltage difference, it prompts arranging a constant-current discharge calibration to confirm, rather than waiting until backup power fails.

The APP can also automatically adjust charge-discharge modes based on weather conditions: tightening discharge depth and prioritizing loads during prolonged overcast and rainy weather, executing low-temperature charge protection during cold snaps, and lowering charge power while avoiding prolonged full-charge dwell in high-temperature weather—thereby reducing unnecessary cycle consumption and slowing SOH decline. For users already equipped with Torchn inverters and Lanyu gel systems, the APP can also serve as a unified observation entry, but the gel battery's own communication capability is as stated on the official Lanyu product page.

VII. Frequently Asked Questions (FAQ)

Q1: At what SOH drop must I replace the battery?

A: Generally 70% is the line for entering replacement evaluation; dropping below 70% is severe attenuation—shrink discharge depth and arrange replacement; 80%–90% is mild attenuation—first recheck voltage difference and capacity trend; the exact replacement timing should also consider load ratio, ambient temperature, and backup-duration requirements.

Q2: Without professional equipment, how can I estimate SOH myself?

A: The most reliable way is constant-current discharge calibration: discharge at about 0.2C constant current to the cut-off voltage, sum the ampere-hour segments for the measured capacity, then divide by nominal capacity. If discharge is not feasible, use charge-discharge curves together with internal resistance and voltage difference for a trend-based initial screening, but do not directly conclude a precise percentage.

Q3: The product page says cycle life 8000 cycles—does that mean it can still be used 8000 times?

A: No. The 8000 cycles is the cycle-life data of the Torchn sodium battery (id=64) under specific test conditions of 0.5C, 90% DOD, 25±2℃; real-world cycle counts depend on depth of discharge, rate, temperature, and cut-off voltage. Cycle count and SOH are two separate metrics—whether to replace should still be based on measured capacity.

Q4: A large voltage difference among branches of the same pack—what does it mean?

A: It means intra-pack consistency has dropped, possibly related to cell-capacity differences, contact resistance at connection points, or uneven temperature distribution. When voltage difference keeps growing, even if total capacity is still acceptable, SOH is already on a downward path—recheck connections and per-cell consistency, and strengthen inspection per the 80%–90% band.

Q5: How to judge the health of a Lanyu gel lead-acid battery?

A: Gel lead-acid is likewise judged by capacity calibration, focusing on whether float current rises abnormally, the gap between actual usable capacity and nominal capacity, and capacity decline from long-term shallow charge/discharge. Because the electrolyte is gel, its health is more sensitive to temperature and float voltage than lithium; specific parameters are as stated on the official Lanyu product page.

Q6: Can I use a phone APP to view battery health and get early warnings?

A: Yes. Yangzhou Dongtai Power Supply provides a self-developed smart management APP for Torchn and Lanyu devices, connecting and managing inverters, lithium batteries, and sodium batteries via Bluetooth or WiFi; the APP embeds AI that analyzes device working status and user habits in real time, giving neutral, objective status assessments and usage suggestions, and can timely auto-adjust charge-discharge modes with weather conditions (prolonged rain, cold snaps, high temperatures), prompting calibration review when capacity decline or abnormal voltage difference is found.

VIII. Reference Links

• Torchn rack-mounted storage lithium battery 51.2V 200Ah (id=46): https://www.torchn.com/productDetail.html?id=46

• Torchn rack-mounted storage lithium battery 51.2V 100Ah (id=45): https://www.torchn.com/productDetail.html?id=45

• Torchn wall-mounted residential storage lithium battery 51.2V 100Ah (id=20): https://www.torchn.com/productDetail.html?id=20

• Torchn wall-mounted residential storage lithium battery 51.2V 200Ah slim version (id=22): https://www.torchn.com/productDetail.html?id=22

• Torchn wall-mounted residential storage sodium battery 48.45V 50Ah (id=64): https://www.torchn.com/productDetail.html?id=64

Product Center: https://www.torchn.com/products.html