Reserve battery collapses during the monthly GMDSS load check
During the monthly GMDSS battery check on a 24 V lead-acid reserve battery (200 Ah, dedicated), you record the following: charger float voltage 27.2 V, charger ammeter near zero; battery open-circuit voltage after 30 minutes 25.8 V. On applying the normal GMDSS load (VHF transmitting 25 W, MF/HF on standby, NAVTEX and DSC), voltage falls to 21.9 V within 90 seconds and the low-voltage alarm sounds. Two cells are warm; electrolyte level in one cell is below the minimum mark; hydrometer readings are 1.120 in that cell and 1.150 in another, against 1.265 for the rest. The battery room smells faintly of acid. The vessel is at anchor outside Lagos, with shore power available, and the emergency generator is tested weekly. The master wants to know whether the battery can be left until the next port and whether the GMDSS watch can continue.
1. Interpret the readings and decide whether the battery is serviceable as the GMDSS reserve source. Explain your reasoning.
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The battery is not serviceable as a GMDSS reserve source. A healthy 24 V lead-acid battery has about 25.5–26.4 V at rest after charging, and each cell about 1.265 SG. Under a modest GMDSS load, 21.9 V is about 1.825 V per cell, which indicates a cell or cells are failing or heavily sulphated. The low SG (1.120 and 1.150) confirms that those cells are not holding charge; a fully charged cell would be near 1.265. Warm cells, low electrolyte, and acid smell suggest overcharging/drying out or an internal short, not merely a discharged battery. The charger ammeter near zero with 27.2 V float could mean the charger is supplying only the load and the battery is not accepting current; check charger output, fuses, and connections. Do not add acid and do not overfill; distilled water is added only after charging, but topping up will not restore capacity. A load test at the manufacturer's specified rate is needed before condemning it, but these readings already show it cannot support the required GMDSS reserve period.
2. What immediate actions should you take to maintain the GMDSS watch and notify the right people?
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Inform the master immediately. Reduce non-essential loads; keep VHF Ch16/DSC, the required MF/HF watch, NAVTEX and Inmarsat available from the best remaining source. If the ship has an emergency generator or an approved alternative GMDSS supply, use it in accordance with the ship's procedures, but do not improvise a connection that bypasses fuses or the battery isolation. Since shore power is available at anchor, the charger can be checked and, if the battery is isolated, a shore technician can attend; however, the GMDSS reserve battery itself must still meet capacity requirements before the ship sails. Notify the company/DPA and, if the required GMDSS capability is degraded, the relevant coast station/port authority as required by the SMS and flag instructions. Maintain a listening watch by the most reliable means and record the defect. Do not leave the vessel at anchor believing the battery will recover by itself.
3. What corrective action and records are required before the vessel sails?
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Replace the battery with the same technology, voltage and capacity, or a manufacturer-approved equivalent. Check the charger's voltage and current output, charging regime, ventilation, and battery-room temperature; repair the fault that caused overheating/drying. Inspect terminals and fuses; verify that the new battery passes a capacity/load test and that the low-voltage alarm and changeover work. Update the battery log, PMS, and official/radio logs; record the defect, temporary measures, replacement date, and test results. If replacement is delayed, the ship should not rely on this battery for GMDSS reserve and the master should consider whether the intended voyage can proceed; the flag/port state may need to be informed. Keep the EPIRB, SART and portable VHF batteries separate and check them as well, because a battery-room fault can affect more than one item.