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Rockyrhodes: You have a brand new 2015 Evinrude E-Tec 90 H.O. outboard on your 2004 Boston Whaler Montauk 170. Your outboard alternator puts out 133 amps total with 50 net dedicated to engine functions. Why do you need a second battery? Your boat's standard configuration criteria has changed now that you have an E-Tec. Unless you want to light up your boat with an abundance of electronics, my opinion is get rid of the second battery. Do you really need a second battery with 133 amps generated from your 2015 E-Tec two stroke outboard?