The internal lithium-iron-phosphate battery from inside the N1C.L1000 UPS.

The voltage curve of a lithium-ion battery is much different than that of a lead acid battery. Lead-based batteries have a more linear discharge, where voltage consistently drops over time.

Lithium-ion batteries, like those in N1C Uninterruptible Power Supply (UPS) systems, will lose voltage on initial discharge, but then the voltage remains relatively steady until right before the battery is exhausted and can no longer power the load. As the battery is nearing exhaustion, the voltage starts to drop rather quickly — within the last few minutes of battery runtime.

If you’re monitoring one of our lithium-ion UPS systems while it’s on battery mode, you can tell the battery is nearing exhaustion simply by watching the voltage. When it starts to drop more rapidly, you know you’ve only got moments left to shut down gear attached to the UPS before the UPS turns off.

The voltage curves below are from some basic in-house testing of N1C 120V L-Series UPS systems, which use our outstanding Lithium Iron Phosphate batteries (LiFePO4).

They show the voltage drop (Y-axis) over time (X-axis) under a consistent resistive load.

Click + to reveal voltage curve charts.

L3000

Hover over data points to see voltages.

1500W power draw, 52% load

L2200

Hover over data points to see voltages.

1500W power draw, 72% load

L2000

Hover over data points to see voltages.

1500W power draw, 80% Load

L1000

Hover over data points to see voltages.

750W power draw, 80% Load