30-minute IT shutdown
2 kW for 30 min at 48 V—~24.5 Ah planning floor before margin.
UPS Battery Calculator
Estimate required battery Ah from load, target runtime, voltage, and efficiency.
Quick answer
UPS battery Ah sizes the DC plant for your target backup minutes. Energy need is approximately load (kW) times runtime (hours), adjusted for inverter efficiency and depth-of-discharge margin, then divided by nominal string voltage (higher V reduces Ah for the same energy). Example: 2 kW for 30 minutes at 48 V with 0.85 efficiency needs about 24.5 Ah before aging, temperature, and parallel-string layout—field banks are usually larger. Use measured kW from the load calculator, confirm voltage with your OEM, cross-check minutes in the runtime calculator, or start from how long will UPS last if backup time is your primary question.
Quick UPS Battery Calculator
Defaults: 48 V string, 0.85 efficiency.
Estimated battery: 24.5 Ah @ 48 V
Planning estimate with 0.85 efficiency; add OEM margin for binding designs.
Advanced UPS Battery Calculator
Quick Examples
DC-path / inverter efficiency for planning (default 0.85).
UPS Battery Results
Engineering disclaimer
Estimates only. Verify with manufacturer battery tables, discharge-rate limits, and review by a qualified professional for binding designs.
Results
Required battery: 24.5 Ah @ 48 V
Default: 2 kW, 30 min, efficiency 0.85.
Explain this result (summary)
- Energy need: ~1.0 kWh AC for 30 min at 2 kW before efficiency.
- Ah floor: ~24.5 Ah at 48 V with 0.85 efficiency—field designs are usually larger.
- Cross-check: Compare minutes in the runtime tool with the same assumptions.
Operational guidance
Typical IT ride-through
30 minutes at 2 kW is a common planning anchor—confirm discharge rate limits with the OEM.
Required Ah vs runtime
| Runtime (min) | Ah @ 48 V |
|---|---|
| 10 | 8.2 |
| 20 | 16.3 |
| 30 (your target) | 24.5 |
| 45 | 36.8 |
| 60 | 49.0 |
People also ask
- How many Ah for 30 minutes? At 2 kW and 48 V with ~0.85 efficiency, the planning floor is about 25 Ah before aging margin.
- Is Ah enough to order? You also need max discharge current, terminal layout, and rack constraints.
- Ah vs runtime tool? This page sizes Ah from target minutes; runtime estimates minutes from known Ah and strings.
- 48 V vs 110 V string? Higher nominal voltage lowers Ah for the same energy—confirm parallel string count and OEM discharge limits.
- Parallel strings and Ah? Field banks often use multiple strings; total installed Ah must still meet C-rate and end-of-discharge rules per vendor tables.
UPS battery planning guidance
- Vendor tables: Final string count and C-rate limits come from battery OEM data (and UPS vendor packs from APC, Eaton, Vertiv class frames)—use this page for planning Ah only.
- Aging margin: Size for end-of-life capacity at the design horizon, not day-one nameplate alone.
- Discharge rate: High-rate bursts may need more Ah than energy math alone—check OEM C-rate limits.
- Depth of discharge: Shallow cycling extends life; planning efficiency should reflect DOD policy, not 100% use of nameplate.
- Runtime cross-check: Enter the same kW, V, and efficiency in the runtime calculator and reconcile minutes ↔ Ah before procurement.
Upstream: load, capacity. Cross-check: runtime. Scenario: how long will UPS last. Neighboring: cable size, voltage drop, breaker size.
Full four-step path: UPS calculator hub (load → capacity → runtime → battery).
UPS battery for common scenarios
15-minute generator bridge
5 kW for 15 min—higher discharge rate; verify OEM limits.
60-minute NAS ride-through
0.5 kW for 60 min at 48 V—light load, longer Ah at the same voltage.
2 kW on 110 V string
30 min at 110 V cuts Ah versus 48 V for the same energy—confirm string count with the OEM.
UPS battery formula (quick reference)
Ah ≈ (kW × 1000 × runtime_min ÷ 60) ÷ (V × efficiency). See formula notes and worked examples below in the depth section.
How to size UPS battery Ah
- Confirm load kW and target runtime minutes.
- Enter string voltage and planning efficiency.
- Read Ah; cross-check in runtime.
Frequently Asked Questions
Why does my UPS vendor software disagree slightly with this page?
Vendors embed chemistry-specific curves, temperature coefficients, and minimum cell voltages. Use this calculator for directional planning, then finalize strings with OEM tools and stamped project documentation where required.
Should I add margin for battery aging?
Yes. End-of-life capacity is lower than day-one ratings; prudent designs reserve Ah so degraded strings still meet the runtime contract at the design horizon.
Does higher inverter efficiency always reduce Ah?
Higher efficiency reduces DC energy required for the same AC load, which lowers Ah at a fixed voltage. Efficiency varies with load level, so use vendor curves near your true operating point.
Is amp-hour the only figure I need to order batteries?
No. You also need maximum discharge current, terminal layout, breaker coordination, recharge current limits, and physical rack constraints—Ah is necessary but not sufficient.
How does this tie to the UPS runtime calculator?
Runtime estimates minutes from known battery parameters; this step estimates Ah when minutes and load drive procurement. Move between the tools as your knowns change.
How it works
Battery amp-hour (Ah) sizing answers whether the DC plant can deliver enough energy for the target minutes at the protected AC load. Conceptually, you convert load power (kW) and required backup time into an energy demand (kWh), translate that to DC watt-hours using practical inverter and cable efficiency assumptions, then divide by the string voltage to obtain an amp-hour requirement before manufacturer derating curves.
Higher DC bus voltage reduces amp-hour for the same energy because each amp-hour carries more watt-hours when multiplied by a larger voltage. Temperature, end-of-discharge voltage, aging, and desired depth of discharge all increase the installed Ah relative to a naive arithmetic estimate—your battery vendor tables remain authoritative for final cell selection.
This calculator is positioned after load and runtime intent are understood. Treat its output as a planning anchor, then validate against UPS manufacturer software, battery tables, and local codes governing ventilated battery rooms and maintenance access.
Formula and sources
Planning anchor: DC energy (Wh) ≈ (Load kW × Runtime hours) ÷ Overall DC-path efficiency; Ah ≈ DC energy (Wh) ÷ Nominal battery voltage (V)
Overall efficiency bundles inverter conversion, cable loss, and conservative headroom; exact factors vary by topology and state of charge.
Always round up to the next commercial block or string count and apply aging margin recommended by the battery OEM.
Worked examples
- Two kW for thirty minutes at forty-eight volts
Half an hour at 2 kW implies about 1 kWh of AC-side energy before efficiencies. At 48 V, the naive amp-hour floor is roughly 21 Ah before inverter loss, temperature derating, and end-of-life margin—field designs normally select a materially larger bank.
- Raising string voltage from forty-eight to one hundred ten volts
For the same energy demand, moving from 48 V to 110 V cuts the amp-hour requirement roughly in proportion to the voltage ratio because watt-hours per string increase with voltage for the same current profile.
- Short five-minute bridge versus thirty-minute ride-through
Five minutes at the same kW needs one-sixth of the energy of thirty minutes, but very short windows still require attention to discharge rate limits—some chemistries prefer longer, gentler discharges than aggressive high-rate bursts.