Starting batteries

Power of starter[kW] Battery capacity [Ah]
due to heating
S1= [mm2],
due to permissible voltage drop
cable length l= , S2=[mm2]


standarised cable: [mm2]

Rated voltage: Type of accumulator battery:
24 V Lead-acid
12 V Alkaline
Temperature of electrolyte:
25 °C, batteries placed on board of ships sailing in the tropical zone,
15 °C, batteries fitted on board of ships sailing in unrestricted zone,
5 °C, batteries fitted on board of ships sailing in unrestricted zone or operated in moderate zone and installed in the engine room or compartments to heated by adjacent rooms,
-15 °C, batteries fitted on board of ships sailing in unrestricted zone or operated in moderate zone and installed in non-heated rooms,
-25 °C, batteries fitted on open decks on ships other than sailing only in the tropical zone.
Temperature coefficient a= , assumed:
Battery capacity is rated at start of one combustion enegine for 6 starts-up taking 5 seconds each. In case when one battery is a source for more than one starter, the total capacity should be calculated as a sum of the required capacity of the greatest starter and a half of the required capacity for each of the remaining starters. Calculations were carried out based on the Polish standard PN-W-89509:1997 Merchant ships, batteries, selection, in accordance with the following equations: aku_start_wzor, where Qr - required of capacity of the starting battery, C - capacity related to the starter power (curves are available in the standard), a - temperature coefficient (curves are available in the standard) taking into account reduction of the capacity due to electrolyte temperature, 0,75 - undercharge coefficient, aku_start_wzor_S1, where S1 - minimum cross-section of the feeding cable due to heating [mm2] Izw - short circuit current in the starter during start-up (curves available in the standard), j - permissible current density shall not exceed 20 [A/mm2] aku_start_wzor_S2, where S2 - minimal cross-section of the cable due to voltage drop related to short-circuit current Izw, [mm2] l - lenght of the cable, [m], Un - rated voltage of starter, [V].   Author: Daniel Czarkowski