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Dear Fellow Raiders,

I have a 40hp outboard and it appears the battery is kaput. I've tried charging it without any luck. I'm just wondering what you would recommend. I only have a sounder and standard Navigation lights to run,




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Hi deek... I guess your question is what capacity battery should you be buying as a replacement?

As a starting point, what battery capacity did you have and what was your experience with that size battery??

If your not sure, Then here is my take:

1) check you motor manual for the recommended CCA (cold crank amps) battery for starting. This is what you want on hand to start your motor effectively.

2) Only you know how long you plan to run your lights + sounder just off the battery. So perhaps check the sounder manual for what current it draws, same for lights (say standard white/red/green nav lights -- estimate 3 x 5watt if they are standard incandescent, less if they are LED).  

Regarding calculating how long your battery will last running just this gear - here's how I would do it :

1) Check the capacity rating of your batteries - you are looking for the Amp hours number

2) Check your equipment consumption - usually a Watt (W) rating and convert that to Amps (A). Use a calculator like the one here, or the formula I=P/V I=AMPS, P=Watts, V=volts (usually 12V in your boat DC circuit)

3) Divide the Battery Amp hours by the equipment draw in Amps and the resulting number is the number of hours that your battery should roughly last.

A lot of this was discussed in a previous post --



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