didn't know it was a trunk mounted batt & that does change things. Always done it since batt moved to trunk? Alot depends on how you wired it and the gauge of the main cables from trunk up front (that causes people alot of issues). You might disconnect the trunk batt & take it up front & jump it to the st relay and eng block & see if it straightens out. Batt fully charged of course. Holler when you can