Calculator
UPS Battery Backup Calculator
Estimate UPS backup time from load, battery voltage, Ah capacity, battery count, and inverter efficiency.
Calculator Inputs
Connected load must be a valid number.
Battery voltage must be a valid number.
Battery capacity must be a valid number.
Legend
UPS backup legend
Battery voltage, amp-hour capacity, and battery count estimate stored energy. Efficiency reduces the theoretical value to account for inverter and system losses.
Input meaning
- Connected load: enter the measured, quoted, or hospital-approved value in W.
- Battery voltage: enter the measured, quoted, or hospital-approved value in V.
- Battery capacity: enter the measured, quoted, or hospital-approved value in Ah.
- Number of batteries: enter the measured, quoted, or hospital-approved value.
- UPS efficiency: enter the measured, quoted, or hospital-approved value in %.
Result interpretation
- Usable battery energy is an approximate watt-hour value after efficiency.
- Estimated backup time is useful for planning, but critical areas need actual discharge testing under controlled conditions.
Assumptions
- Battery age, temperature, discharge rate, and UPS design affect actual runtime.
- Critical life-support loads need professional electrical review.
Biomedical use
- Useful for ICU, OR, lab, imaging workstation, network rack, and medical gas alarm backup planning.
How to identify the required values
Use these examples and common working ranges to choose values from gauges, labels, manuals, datasheets, RFQs, service reports, CMMS records, or hospital planning assumptions.
| Field | Example value | Common range | Tip |
|---|---|---|---|
| Connected load | Monitor 80 W + workstation 250 W = 330 W. | Small medical devices may be 20-500 W; workstations, UPS loads, and carts may be 300-2,000 W. | Use measured watts where possible; nameplate values may not represent real running load. |
| Battery voltage | 12 V per battery, or 48 V battery bank depending on UPS wiring. | Common batteries are 12 V blocks; UPS strings may be 24, 48, 96 V, or higher. | Use total battery bank voltage if batteries are wired in series. |
| Battery capacity | 12 V, 9 Ah battery label means capacity is 9 Ah. | Small SLA batteries are often 7-18 Ah; larger packs may be 40-200 Ah or more. | Use rated Ah only for healthy batteries; derate old batteries. |
| Number of batteries | Example: 1. | Enter the actual installed count; for UPS strings this may be 2, 4, 8, 16, or more batteries. | Use the actual number contributing to the calculation. |
| UPS efficiency | Use 85% if actual UPS efficiency is unknown. | Many UPS planning estimates use 80-90% unless vendor data is available. | Use the vendor value if known; otherwise use a conservative planning value. |
Common ranges are starting points for hospital planning. For final procurement, acceptance testing, electrical design, medical gas design, radiation shielding, dialysis water systems, or clinical use, replace the example values with site-specific data and vendor-confirmed figures.
Input Checklist
Confirm these values before relying on the output for procurement, PM, or service planning.
- Load watts
- Battery voltage
- Battery capacity
- Battery count
- Efficiency
Safety And Engineering Notes
Use calculator outputs as planning estimates and verify critical systems with calibrated measurement or qualified engineering review.
- Battery age, temperature, discharge rate, and UPS design affect actual runtime.
- Critical life-support loads need professional electrical review.
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