I fly a Vans RV 6-a. 12 volt system, Lycoming IO 360. Installed new battery, duplicating exactly make/model that was in the aircraft. When I go to the engine page, the bar showing the charge shows "10" without alternator on and when I turn on the alternator it goes downward and shows a "-15". When I went in the setup pages under maintenance/calibration, one of the two pages, namely the second page had all zeros. Two questions; is the -15 normal and does anyone have recommendation under the maint/calibration pages for data entry factors?