How long does a UPS battery last?

People ask this about two things: how many years the battery lasts, and how many minutes it runs during an outage. Here are both.

Lifespan in years

A sealed lead-acid UPS battery lasts about 3 to 5 years. Lithium-ion batteries last longer, often 8 to 10 years. Heat is the biggest enemy. A UPS kept in a hot room can lose capacity in two to three years.

Runtime in an outage

Runtime depends on battery capacity and load. A rough formula for estimating:

Runtime in hours = battery watt-hours × inverter efficiency × usable fraction ÷ load in watts

Example: a UPS with 216 watt-hours of battery, 85 percent inverter efficiency and 80 percent usable capacity has about 147 watt-hours to use. At a 300 W load, that is about half an hour. Real results are often lower as the battery ages, so use the manufacturer's runtime chart.

Typical runtime

• Router and modem: one to several hours.
• Desktop PC and monitor: 10 to 30 minutes.
• Gaming PC under load: a few minutes.
• Server rack: depends on added battery packs.

What shortens battery life

• High temperature.
• Frequent outages.
• Running near full load.
• Poor ventilation.

Signs it needs replacing

• Runtime drops sharply.
• The UPS beeps or shows a battery light.
• The battery fails a self-test.
• The case bulges.

Replace the battery every 3 to 5 years even if it still seems fine. Many APC and other brands sell replacement cartridges that you can install yourself.