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Old 06-06-2020, 12:13 PM   #5
Ski in NC
Technical Guru
 
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City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
Engine mfr's always like to spec high capacity batts in their manuals, partly to avoid complaints and also they don't know how cold conditions might be where it is operated.

I've seen the same CCA spec for a given engine in both the marine version and the standby generator version. The standby gen version could be used up in the arctic in sub-zero temps. The marine version, not so much. Takes way less batt to start at 40F than at -40F. Spec is the same for both.

In my shop, the go-to bench test batt is a simple grp 31. Starts every engine every time (unless 24v, then I need another).

On my personal boat which has an 8.3 liter engine, it starts also on a single grp 31, I think around 900 CCA. Starts fine down to 40F, which is the coldest engine temp I have run the boat. Spec for my engine is 1800 CCA. So I am at half spec and it is fine.

For your 3.7 liter engine, a 31 will be fine. Fitting it, I know those euro boxes can be a problem. You could go even smaller if needed to fit in the box.
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