Sounds like dirty battery connections. Disconnect negative battery cable first. Clean the post and connector with a small wire brush. Disconnect positive battery cable and clean post and connector with a small wire brush. Add a small amount of battery terminal grease to the posts and connectors. Install the positive cable first and then the negative. Repeat for every battery. If you have the type of connectors that pinch the battery cable under a plate to make connection to the connector, you also have to remove the wire from the connector, clean, and grease.
Orrr, take it back to the installer and have them clean the terminals and add grease before reassembly.
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Cliff
2011 Four Winds Chateau 23U