Battery autonomy is the period of time (in minutes or hours) a UPS battery will last for at a specified load level in the event of a power outage. In essence, it is how long the inverter will run off battery power.

Autonomy can also be referred to as backup, discharge time, or runtime. It is a function of battery charge state, load size, and capacity. 

UPS battery autonomy can support loads for just a few minutes through to several hours, although for longer runtime applications, it is more cost-effective to combine a UPS with a backup generator. 

Adding extra battery strings connected in parallel will increase autonomy, although it is important to consider the charging capabilities of the UPS. 


How Is UPS Battery Autonomy Calculated?

To size a UPS battery correctly, battery runtime is a factor of the Ampere-hour (Ah) rating of the battery set and the applied load – the lower the load, the longer the runtime for a specific Ah rating.

For example, a 10 kVA/8 kW three-phase UPS with a 14Ah battery set will offer approximately 15 minutes runtime at full load. But this might be extended to 30 minutes or more when powering a reduced load, such as 5 kVA/ 4 kW i.e. 50% capacity.


Further Reading: 



Lifespan of ups batteries

Batteries are essential for UPS correct functioning. In this whitepaper we explain the main important factor that affect their duration and we provide some recommendations for optimizing the UPS + batteries system, in order to maximize its lifespan and general availability.