How long will my UPS run on battery?
Runtime depends on the real load in watts, the battery string voltage and capacity, the inverter efficiency and the discharge-rate effect. A rough estimate: convert watts to battery current (P ÷ (V × η)), then apply Peukert's law to the rated capacity. For final sizing, use the battery maker's constant-power discharge table.
Watts, not VA
UPS ratings are often given in VA. Runtime depends on real power (W). Read the load on the UPS display or measure it.
Why runtime is shorter than expected
Lead-acid capacity falls as discharge current rises (the Peukert effect). A battery rated at 20 hours can deliver a much smaller share of its amp-hours in a 10-minute discharge. Ageing reduces it further; IEEE 485 sizing practice adds a 1.25 ageing factor (size for 80% remaining capacity).
Replace all batteries of a string at the same time.
Match voltage, capacity, case and terminal type to the UPS manufacturer's specification.
Heat shortens VRLA battery life; keep the UPS ventilated.
Real references in our catalogue
No reference in our catalogue matches this category yet. We only list batteries whose specifications we could take from a manufacturer document.
Data Sources & LicencesFrequently asked questions
Can I add a bigger battery to get more runtime?
Only if the UPS manufacturer supports external battery packs or that capacity: its charger and thermal design are sized for specific batteries.
What is the Peukert exponent?
A number (usually above 1 for lead-acid) describing how much capacity is lost at higher discharge currents. 1.00 means no loss. Derive it from two published discharge times or take it from the datasheet.