Also in Use when you are driving down the road or the engine's alternator will not charge the house batteries. To echo Jamie -- ALWSYS in USE unless it is being stored (and if you have it plugged in to store power then it should be in USE. Remember, house batteries will not charge unless it is in USE and house batteries will totally discharge if you store it in USE.
Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)