UPS String Capacity Test
UPS String Capacity Test: convert a timed discharge into measured Ah, kWh and state of health.
Data-centre VRLA strings under IEEE 1188: run a rated-current discharge to the end voltage, measure the delivered capacity, and read the string-level state of health — the trigger to plan replacement is the IEEE 80%-of-rated threshold.
SoH = measured Ah ÷ rated Ah at the same discharge rate and temperature. Rate matters — discharging a lead-acid battery faster than its rating undercounts capacity (Peukert effect; see the Peukert tool), so always test at the datasheet rate.
Engineering estimate from published standards and typical equipment data. Site conditions, equipment datasheets and measured data govern the real result — confirm with a qualified engineer.
Use the free UPS String Capacity Test online — UPS String Capacity Test: convert a timed discharge into measured Ah, kWh and state of health. Runs instantly in your browser: no signup, no upload, mobile-friendly.
About UPS String Capacity Test
Data-centre VRLA strings under IEEE 1188: run a rated-current discharge to the end voltage, measure the delivered capacity, and read the string-level state of health — the trigger to plan replacement is the IEEE 80%-of-rated threshold.
How to use UPS String Capacity Test
- 1Charge fully and rest the battery, then discharge at the rated test current.
- 2Time the discharge until the cutoff voltage and enter current and hours.
- 3Read measured Ah, energy delivered and SoH against nameplate.
Why use UPS String Capacity Test?
- ✓The ground-truth method every warranty and standard recognizes
- ✓Correct test rates for your battery class baked into the help text
- ✓Converts the timed discharge into Ah, kWh and SoH automatically
- ✓IEEE/IEC-aligned procedure notes prevent the classic testing mistakes
Frequently asked questions
How do I properly test battery capacity at home or on site?+
Full charge, rest 1–4 hours, then a constant-current discharge at the datasheet rate (C/20 for lead-acid, C/3–1C for lithium) down to the specified cutoff voltage, timing it. Measured Ah = current × hours. The biggest error is testing at the wrong rate — lead-acid reads dramatically lower at high currents.
What discharge rate should I use for the test?+
The rating's basis: most lead-acid ratings are C20 (a 150 Ah battery tests at 7.5 A), traction batteries C5, lithium typically C/3 or 1C per datasheet. Testing faster than the basis undercounts capacity (Peukert effect) and falsely fails healthy batteries.
How often should batteries be capacity-tested?+
Standby/UPS strings: yearly per IEEE 1188 practice, quarterly once past 80% of design life. Cycled banks (solar, traction): every 6–12 months. EVs: at purchase/sale and yearly. Consistent method and temperature matter more than frequency — trends need comparable points.
Can I trust the BMS SoH reading instead of testing?+
Partially. Good BMS estimates track within ±5% when the pack regularly sees full cycles; they drift badly on shallow-cycled packs that never let the BMS recalibrate. A periodic measured test anchors the BMS estimate — and is the only number a warranty process accepts.
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