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I agree with Richard on the merge switch use. IMO it's much better to just add an Amplstart or other brand that takes power from the house batteries (which are usually charged by the inverter or if you have solar) and sends a small charge to the chassis batteries.
These devices have an automatic cutoff that will not let the chassis batteries charge if the house batteries are below a certain voltage. Cheap insurance.
BTW if you have a Power Pulse on your batteries then this device is not the same as the above and does consumer power from the batteries it's hooked up to.