What reserve capacity must a battery have if it is required to supply the following emergency services for a period of 4 hours? It should be assumed that under emergency conditions the stated pumps will be required to operate continuously.
• Navigation lights requiring 300 Watts • Escape lighting totaling 1.2 kW • Emergency bilge pump of 850 Watts • Emergency fire pump of 1.5 kW

 

(300W+1.2kW+850W+1.5kW)*4h = 3.85kW*4h = 15.4 kW-h

Assuming 12V cells assuming 70% conversion efficiency from inverter:
(3.85kW)*4h/70%/12V = 458.3A*4h = 1833.2 amp-hours

This is a good read now: http://en.wikipedia.org/wiki/Peukert's_law

 

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