UPS Runtime Calculator

Manufacturer runtimes are measured with new batteries at 25°C under ideal lab conditions. Real-world runtimes are shorter for several reasons: battery aging (lead-acid batteries lose 20–30% capacity after 2–3 years), temperature (every 10°C above 25°C halves battery life and reduces capacity), actual load type (motors and hard drives draw surge current on startup), and UPS conversion losses. This calculator's health factor accounts for battery aging — set it accurately for realistic results.

Start by listing all equipment that will be connected and their watt ratings (found on the nameplate or spec sheet). Add 20–25% overhead for startup surges and future equipment additions. Then choose a UPS whose watt rating (VA × Power Factor) comfortably exceeds that total. Never load a UPS above 80% of its rated capacity — doing so reduces battery life, increases heat, and risks overload shutdown. For servers with high-efficiency power supplies, use the actual measured draw rather than nameplate maximum.

VA (Volt-Amperes) is the apparent power — the product of voltage and current. Watts is real power — the actual energy consumed. The difference is the power factor (PF). Most electronic equipment has a PF between 0.6–0.9. A 1500VA UPS with 0.8 PF delivers 1200W of real power. Always compare your load in Watts against the UPS watt rating — not VA. Many cheaper UPS units only show VA, hiding a low power factor.

Most sealed lead-acid (VRLA/AGM) UPS batteries last 3–5 years under normal conditions. Replace when: the UPS self-test fails repeatedly, runtime drops below 50% of original, the battery is physically swollen or leaking, or the UPS is more than 4 years old. For critical systems (servers, NVR, medical equipment), replace proactively at 3 years regardless of apparent condition. Lithium-ion UPS batteries last 8–10 years and are increasingly available as replacements for traditional UPS units.

Yes — many mid-range and enterprise UPS units support external battery modules (EBMs) that connect directly to the UPS and appear as additional internal batteries. Some units also support custom external battery strings using matching voltage batteries connected to the UPS battery terminal. Extended battery configurations are common for NVR systems, small server rooms, and network closets where 30+ minutes of runtime is needed. Always use the same battery type and voltage as the internal batteries, and ensure the UPS charger can handle the increased Ah capacity.

For a typical NVR-based CCTV system: NVR unit (30–80W) + HDDs already counted in NVR power + PoE switch (50–200W depending on camera count and wattage) + managed switch or router (15–30W). Budget 15–25W per PoE IP camera at the switch level. A 16-camera system with a NVR and PoE switch typically draws 120–280W total. A 1000–1500VA UPS provides 15–30 minutes of runtime on this load — enough for graceful shutdown or generator start. See the CCTV Storage Calculator for full system sizing.