PAVA Standby Battery CalculatorBeta

What it calculates

The minimum battery capacity for a voice alarm system to BS 5839-8:2023, Annex C: enough to run the system quiescent for the standby period (normally 24 hours), then broadcast at full alarm load for the alarm period (minimum 30 minutes), with the standard's 1.25 allowance for ageing and temperature. The result is the capacity at the 20 hour rate (C20) that the battery bank must equal or exceed.

The number the standard won't give you

Annex C requires derating factors taken "from the battery manufacturer's data", then admits in the same breath that this data is often not available. That is the number this calculator supplies. It derives the factors from whatever the datasheet does publish: the manufacturer's constant-current tables where they exist, Peukert's law where they do not, and it always tells you which source it used. The answer is only as good as its source, so the calculator ranks them for you, best first: manufacturer table, then a Peukert fit from rating points near the alarm duration, then a fit from long-duration points (floored for safety), then a conservative default.

Which level to use, and when to move up

Start at Level 1. Two questions, a first estimate, and every assumption it made listed beside the answer, so you can see exactly what it guessed on your behalf.

Move up to Level 2 once you have the real system data: loudspeaker load, quiescent current, battery voltage. This is the level most design work needs.

Use Level 3 when you have the full picture: site measurements from an existing system, an unusual message cycle, or a specific battery whose datasheet you want the calculation built on.

You do not have to choose the right level first time. Start simple and climb as the information arrives; each level carries the same result forward and takes it further.

One thing worth knowing before you specify a battery. The lighter levels protect you by assuming the worst: Level 1's guesses are deliberately conservative, so its answer usually sits above the real requirement. Feed in measured data at Level 2 or 3 and the number often comes down, sometimes to a smaller, less expensive battery that still meets the standard in full. Refining is not only about a more accurate figure; it can stop you fitting more battery than the system actually needs.

Before you rely on the result

The output is a calculation record, not a certificate. Verify the inputs against the installation, check the battery manufacturer's published data, and never size below the voice alarm equipment manufacturer's certified minimum battery or outside the charger's limits. Battery standby capacity is a life-safety calculation and final responsibility rests with a competent person. Questions, or want us to run the calculation with you? contactus@proaudium.com.