Yamaha SX Jet boat maintenance and upgrades questions

[dlazic1979bg]

Hello - First-time boat owner. I live in PA, so the boat is already winterized, but I have questions for spring maintenance(counting days). I have a 2016 SX192, and the previous owner told me he replaced coils, spark plug, and oil every year. Spark plug and oil I get, but do we need to replace coils every year? Original Yamaha coils (6S5-82310-10-00) are over $300. Is Amazon/Ebay a safe place for that? Do you guys have any suggestions on best practices/websites for coils? Any other recommendations besides what's already in the official manual?
Second question - did anyone add an additional battery to the SX line? I am always concerned about what if my battery dies, I have small kids. I did order a battery jump unit. I just wonder if anyone has already got a second battery installed and how they did it. Thank you, guys

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[Neutron]

Coils only replaced when they go bad. Yearly maintenance is oil, filter, and spark plugs. Every 100 hours i would pull the pump cone and inspect the grease for water intrusion, reinstall cone with new oring

Some with the factory single battery have added a second. If it was me, i would. Not that difficult depending on the switch setup you use