Starting battery selection

Battery capacity is rated for the start of one combustion engine, six startups of 5 seconds each. Where one battery is the source for more than one starter, total capacity should be calculated as the sum of the required capacity of the largest starter plus half the required capacity of each remaining starter.

Calculations follow the Polish standard PN-W-89509:1997 — Merchant ships, batteries, selection, in accordance with the following equations.

• Qᵣ — required capacity of the starting battery
• C — capacity related to starter power (curves in the standard)
• a — temperature coefficient (curves in the standard), reduction of capacity due to electrolyte temperature
• 0.75 — undercharge coefficient

• S₁ — minimum cross-section of the feeding cable due to heating [mm²]
• I_zw — short-circuit current in the starter during startup (curves in the standard)
• j — permissible current density, not to exceed 20 A/mm²

• S₂ — minimum cable cross-section due to voltage drop related to short-circuit current I_zw [mm²]
• l — length of the cable [m]
• Uₙ — rated voltage of the starter [V]

This page is reference only: the temperature and starter power coefficients (C, a) come from curves in the standard rather than a closed-form equation, so no interactive calculator is provided here.