EN 12845 Monthly Routine — Battery Checks

The standard devotes the single normative item of the monthly visit to one thing: the lead-acid cell — the diesel pump starter battery and the control panel standby battery. When this is skipped on site, the diesel becomes a pump that will not turn over, and in a fire there is no recovering from that.

At a food factory the diesel pump failed to crank during the annual test. The battery display read 24 V, the terminals were tight, and the control panel showed a healthy status light — but as soon as the starter engaged, the voltage collapsed to 8 V. Opening the battery revealed two dry cells with oxidised plates at roughly half their rated capacity. The battery was there and the form said "OK", but nobody had measured electrolyte specific gravity in eighteen months. The single paragraph of Clause 20.2.3 exists to prevent exactly that failure.

Clause 20.2.3 — what the standard says

All lead-acid cells — including those serving diesel engine starter batteries and control panel power supplies — are to be checked for electrolyte level and specific gravity. If the specific gravity is low, the charger is to be checked; if the charger is operating normally, the affected battery or batteries are to be replaced.

That paragraph carries three explicit instructions: check the level, check the specific gravity, and if it is low, suspect the charger first and replace the battery second.

Which batteries fall within scope?

• Diesel pump starter batteries — two independent sets are mandatory (typically 2 × 12 V or 1 × 24 V). Both are checked at the same visit.
• Control panel standby battery — serving the pump controller or fire monitoring panel. These are usually maintenance-free VRLA units, in which case the specific-gravity part of the clause does not apply and voltage measurement substitutes for it.
• Emergency lighting and control batteries — in scope where they exist in the sprinkler room.

Hydrometer measurement on flooded cells

A hydrometer is a small glass float in a syringe body; drawn into a cell, the electrolyte lifts the float and the scale reads specific gravity. Practical values:

• 1.265–1.285 — fully charged at 25 °C
• 1.225–1.250 — 75–90 % state of charge; acceptable
• Below 1.200 — under 50 % charge. Check the charger first.
• More than 0.030 difference between cells — one cell is dead; replace the battery

Temperature correction: add 0.007 for every 10 °C above 25 °C and subtract 0.007 for every 10 °C below. In a pump room at 35 °C in summer and 8 °C in winter, the raw reading has to be interpreted accordingly.

Electrolyte level

The level should sit 10–15 mm above the plates. If low, top up with distilled water only — never tap water, whose minerals precipitate onto the plates. Confirm the charger is connected before topping up, and allow an hour of charging afterwards so the electrolyte mixes evenly.

Checking the charger — the first step when gravity is low

With a multimeter:

• Charger output voltage: 13.8 V float or 14.4 V boost for a 12 V battery; double that for 24 V
• Charging current: roughly 50 mA float into a fully charged battery. Zero current means a failed charger.
• Any fault LED or display indication

If the charger is behaving normally and the battery still drifts down, the battery has reached end of life. Nominal lead-acid life is four to six years; in a hot diesel pump room, three years is realistic.

VRLA (maintenance-free) batteries

Most modern diesel pump cabinets use VRLA cells that cannot be opened, so a hydrometer is not usable. Clause 20.2.3 does not apply directly; the field practice is:

• Open-circuit voltage ≥ 12.6 V (≥ 25.2 V for a 24 V set) indicates a healthy cell
• Terminals torqued to 8–10 N·m, with no oxidation
• No swelling or bulging of the case
• A dated replacement label present
• Year-on-year comparison with an internal resistance meter, where one is available

Replacement interval should not exceed four years, and three years in a hot climate.

Field error — terminal oxide masked by open-circuit voltage

At a textile factory the monthly form recorded "battery voltage 24.3 V, OK" every month. The annual diesel start test failed. When the terminal was stripped, a 2 mm layer of copper oxide and grease was found underneath. The multimeter was reading an unloaded battery; as soon as the starter drew 200 A, the oxide layer heated, arced and dropped the voltage to nothing. Monthly checks should include a measurement under load, and terminals should be stripped and cleaned at least annually.

Monthly round check list

• Diesel battery 1: electrolyte level, specific gravity per cell, voltage.
• Diesel battery 2: the same.
• Control panel standby battery: voltage and visual inspection.
• Charger status LED, output voltage, charging current.
• Are the terminals clean?
• Battery label date — how much life remains?
• Does the pump room ventilation work (for hydrogen released by the cells)?
• Has the month-end logbook entry been signed?

Comparison with NFPA 25

NFPA 25 places diesel battery checks on a weekly cycle — level, terminals and specific gravity. EN 12845 moves specific gravity to a monthly interval. The practical difference is that NFPA is stricter, while EN 12845 lightens the weekly load in favour of a deeper month-end inspection. In the field, the EN cadence is generally adequate, since the weekly round already covers gauges and the start test.

Link to Turkish regulation

BYKHY defers periodic maintenance to TS EN 12845, so if the monthly battery check does not appear in the logbook it is recorded as a missing record. External insurance auditors ask about this item more than almost any other — if the diesel pump has not survived, the whole system is effectively dead.

Frequently Asked Questions

What is the one normative item in the EN 12845 monthly visit?

Checking every lead-acid cell — diesel starter batteries and control panel supplies — for electrolyte level and specific gravity, and acting on a low reading.

What specific gravity indicates a healthy cell?

1.265–1.285 at 25 °C for a fully charged cell. Below 1.200 means under 50 % charge, and a spread of more than 0.030 between cells means one cell has failed.

If specific gravity is low, do you replace the battery?

Not first. Check the charger — output voltage and charging current. Only if the charger is operating normally does the standard call for replacing the battery.

How do you check a maintenance-free VRLA battery?

By open-circuit voltage (≥ 12.6 V per 12 V unit), terminal condition and torque, case condition, and the dated replacement label. Replace within four years, or three in a hot pump room.

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