From what I understand, there is a charge line running to the chassis battery so that it will charge when plugged in. In addition there is an "emergency start switch" so that if you were to deplete the chassis battery, you can push the button while turning the key, using the house batteries to start the engine.
The water filter is a "whole house" filter. (all water). I know that some people have taken the filter out of the system if they are on city water and the pressure is not high enough.
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