Battery Test

Well it's me again - new to all of this and certainly appreciate the help. I am wondering how to test the state of the battery charge. I am hooked up in the yard still and I put a 4 yr old deep cycle in the unit after charging in the house

When I hit the test button just below the sink, all 4 of the battery lights light up. I am thinking that this means the battery is fully charged and that if it started losing its charge, the green light would go off, then the yellow etc

Is this correct or should only one light be lighting up to indicate the state of charge? Sounds like a stupid question I know but as I said this is all new to me

thanks in advance for your help

jimBOW - Bow Washington