 Fire investigators say the causes of a pair of commercial building fires in Newcastle County over the weekend were accidental. A fire at Tri-State Battery on Old Baltimore Pike in the Industrial Park on Friday night caused by a malfunctioning lithium-ion battery. That blaze cost $75,000 in damage. Fire in a building at the Delaware Solid Waste Authority on Lampson's Lane Saturday afternoon sparked by an unknown heat source that ignited combustibles resulting in $100,000 in damage. Peter MacArthur, WDEL, Delaware's News Radio.