UPS Runtime Calculator

A battery bank does not deliver its rated amp hours to an alternating current load, because the inverter takes a cut, lead acid cells should not be run flat, and a heavy discharge pulls less total charge out of the battery than a slow one. Enter the bank capacity, the system voltage, the load in watts, the inverter efficiency and the depth of discharge, and the tool returns the runtime in hours and minutes along with the current the bank is actually supplying. The Peukert exponent is an input rather than a hidden assumption, so leaving it at 1 gives the plain arithmetic and raising it into the 1.1 to 1.3 range that lead acid cells show gives the shorter, more realistic answer. A second action works backwards from a runtime you need to the amp hours that would deliver it.

Calculator Type

Bank capacity, system voltage and load in, backup time out.

Batteries in parallel add their amp hours. Batteries in series raise the voltage and leave the amp hours alone, so enter the capacity of one string, not the sum of the blocks in it.
The voltage of the bank as wired, not of one cell. Four 12 V blocks in series make a 48 V bank.
The real draw of the kit on the UPS, which is usually well under the plate rating. Measure it if you can.
A decent line interactive or online inverter runs 85 to 95 percent at a sensible load, and worse at very light loads.
How far down you are willing to take the bank. 50 for lead acid, 80 to 100 for lithium iron phosphate.
Leave at 1 for the plain arithmetic. Flooded lead acid is roughly 1.2 to 1.3, AGM about 1.1 to 1.2, lithium about 1.0 to 1.05.
The discharge time the amp hour figure was measured over. Almost every battery is rated at 20 hours, written C20. UPS blocks are sometimes rated at 10 or even 5.
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The other direction: you know the load and how long it has to stay up, and you want the amp hours that would do it.

The real draw of the kit on the UPS, which is usually well under the plate rating. Measure it if you can.
The voltage of the bank as wired, not of one cell. Four 12 V blocks in series make a 48 V bank.
A decent line interactive or online inverter runs 85 to 95 percent at a sensible load, and worse at very light loads.
How far down you are willing to take the bank. 50 for lead acid, 80 to 100 for lithium iron phosphate.
Leave at 1 for the plain arithmetic. Flooded lead acid is roughly 1.2 to 1.3, AGM about 1.1 to 1.2, lithium about 1.0 to 1.05.
The discharge time the amp hour figure was measured over. Almost every battery is rated at 20 hours, written C20. UPS blocks are sometimes rated at 10 or even 5.
Used only to turn the answer into a number of blocks, counted in parallel at the system voltage.
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