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: real equipment load in watts, preferably measured rather than taken only from nameplate.
- Battery voltage and capacity: use the battery bank values actually installed in the UPS.
- Battery count: number of batteries contributing to the runtime calculation.
- Efficiency: approximate UPS/inverter efficiency as a percentage.
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 health is normal and batteries are fully charged.
- Temperature and discharge rate do not significantly reduce capacity.
- Load remains constant during backup operation.
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 to choose values from gauges, labels, manuals, datasheets, or service reports.
| Field | Example value | Tip |
|---|---|---|
| Connected load | Monitor 80 W + workstation 250 W = 330 W. | Use measured load from a power meter when possible; nameplate values may overstate or understate real load. |
| Battery voltage | 12 V per battery, or 48 V battery bank depending on UPS wiring. | Use the effective bank voltage if the UPS battery string is wired in series. |
| Battery capacity | 12 V, 9 Ah battery label means capacity is 9 Ah. | Read Ah from the battery label; old batteries may deliver much less. |
| Efficiency | Use 85% if actual UPS efficiency is unknown. | For critical loads, verify runtime by controlled discharge testing. |
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.