# StandbyCalc Battery Calculator — Fire & Intruder Alarm BS 5839

> Fire & Intruder Alarm BS 5839 (iPhone/iPad app by D4N LTD.)

- Source: https://appshunter.io/ios/app/standbycalc-battery-calculator/id6761339878 (this page in markdown: same URL + `.md`)
- Developer: [D4N LTD](https://appshunter.io/developer/1212131887)
- Category: Utilities, Productivity
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 17.0 · 3 MB
- Languages: American English
- Released: 2026-04-01
- Data updated: 2026-10-24

## What is StandbyCalc Battery Calculator?

StandbyCalc works out the standby battery you need for UK fire and intruder alarm systems in seconds.

Enter the quiescent and alarm currents, pick the fire alarm category or the intruder alarm grade, and get the minimum battery capacity in Ah plus the next standard SLA battery size. Add the fitted battery to see whether it's above or below the calculated minimum. Every battery calculation is free. No ads, no tracking, no sign-up and no subscription.

FIRE ALARM BATTERY CALCULATION
- Based on BS 5839-1
- Categories L, M and P
- 24 h standby, or 6 h where a standby generator is fitted
- Category P premises left unoccupied: standby periods up to 72 h

INTRUDER ALARM STANDBY
- Based on BS EN 50131 and BS 9263, Grades 1 to 4
- BS 4737 (legacy systems) for older installations
- Standby battery sizing for control panels and remote power supplies

PSU AND SLA BATTERY SIZING
- Standalone 12 V and 24 V power supplies with your own standby and alarm periods
- Minimum Ah with de-rating applied, rounded up to the next standard SLA battery

HOW IT WORKS
1. Enter the panel and device currents for standby and alarm
2. Choose the system type, then the category or grade
3. Read off the minimum capacity and the SLA battery to fit
4. Optional: enter the fitted battery to see if it's above or below the calculated minimum

The working is shown in full:
C = 1.25 x (I1 x T1 + D x I2 x T2)

NEW IN 1.0.5
- Fitted battery: enter the fitted Ah and battery date, see whether it's above or below the calculated minimum, and copy a one-line result for your service sheet (free)
- Fitted battery line on PDF reports (Pro)
- BS 4737 now labelled "BS 4737 (legacy systems)"

STANDBYCALC PRO (one-off £9.99)
- Redesigned branded PDF reports with your logo
- Full formula working on every report
- Save calculations against a site and come back to them later
- A clear PDF record of each calculation for your job file

Built for UK fire and security installers, engineers and maintainers who need a quick standby battery calculation on site. Always check results against the panel and battery manufacturer's data.

From D4N LTD. Support: https://d4n.io/projects/standbycalc/

Independent app, not affiliated with or endorsed by BSI.

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| StandbyCalc Pro | $9.99 | one-time |


## Is StandbyCalc Battery Calculator safe?

Not enough ratings yet to assess StandbyCalc Battery Calculator.

## Is StandbyCalc Battery Calculator legit?

StandbyCalc Battery Calculator appears legitimate, with a few gaps. The AppsHunter Legitimacy Score for StandbyCalc Battery Calculator is 65 out of 100 points across 7 verification signals from App Store and developer data.


## Version history (last 5 releases)

### 1.0.5 — 2026-10-19

What's new in 1.0.5:
- Fitted battery: add the fitted battery's Ah (and, if you like, its date) on the fire, intruder and PSU forms to see whether it's above or below the calculated minimum, then copy a one-line result for your service sheet. Free.
- PDF reports now include the fitted battery line (Pro)
- PDF working tidied so every printed step adds up exactly
- BS 4737 is now labelled "BS 4737 (legacy systems)" and sits at the end of the grade list
- Pro is recognised more reliably when the app starts
- Restore purchase now tells you clearly whether Pro was restored, there was nothing to restore, or it couldn't connect
- Wording and layout tidied

Enjoying StandbyCalc? A quick rating really helps.

### 1.0.4 — 2026-10-19

What's new in 1.0.4:
- Saved sites (Pro): keep each calculation under its site and pick up the last visit in one tap
- Redesigned branded PDF reports with your logo (Pro)
- iPad fixes: the upgrade screen, PDF preview and More from D4N now fit properly
- New More from D4N screen with our other trade apps
- iCloud sync fix
- Fixed a double keyboard on iPad

Enjoying StandbyCalc? A quick rating really helps.

### 1.0.2 — 2026-10-18

No more ads. Clearer PDF reports: your name and the site now appear on every report, and empty fields are left out. Battery figures now match between the app and the PDF. Small wording and design fixes.

### 1.0.1 — 2026-08-11

Performance improvements and bug fixes.

### 1.0 — 2026-04-01

No release notes.

## Apps similar to StandbyCalc Battery Calculator

| App | Rating | Price | Category |
| --- | --- | --- | --- |
| [CSL My Base](https://appshunter.io/ios/app/csl-my-base/id1479184708) | — | Free | Utilities |
| [SmartCell Guide](https://appshunter.io/ios/app/smartcell-guide/id6471679545) | — | Free | Utilities |
| [Speedcert](https://appshunter.io/ios/app/speedcert/id6756948281) | — | Free | Utilities |
| [SVL App](https://appshunter.io/ios/app/svl-app/id1550283314) | — | Free | Utilities |
| [Calipsa](https://appshunter.io/ios/app/calipsa/id1480554843) | 5.0 (2) | Free | Utilities |
| [LEWDEN Connect](https://appshunter.io/ios/app/lewden-connect/id6502591368) | — | Free | Utilities |

## More apps by D4N LTD

- [Laylo](https://appshunter.io/ios/app/laylo/id6761607186)
- [GroundPin: Utility Locator](https://appshunter.io/ios/app/groundpin-utility-locator/id6762096562)

All apps by D4N LTD: https://appshunter.io/developer/1212131887

---

*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-24.*