Pretty much everything you need to get a dual battery kit dialed in.

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IF YOU NEED SOLAR, the solar controller we have used with great success is the Victron Energy SmartSolar line of products. We are not big enough to be dealers for them, but this particular model (Amazon store link) https://amzn.to/34Ukpib has worked great for us, and many customers.

Recently came across this cool app from Blue Sea called "Circuit Wizard" for helping to determine wire size and a few other useful tasks:

iOS: https://apps.apple.com/us/app/circuit-wizard/id576865083

Google Play: https://play.google.com/store/apps/details?id=com.bluesea.android.circuitwizard&hl=en_US&gl=US