both deep cycle battery’s are fully charged
you need cranking batteries to crank an engine, deep cycles may work for a while but are not designed for continual cranking duty
deep cycle = house battery (slow amp draw and slow recharge)
cranking battery = engine battery (quick heavy amp draw)
a deep cycle may show a good charge and even pass a load test but isn't designed to handle hard fast amp draw like a bbc will require
as also stated, check your connections and check out the sticky on engine starting systems at the top of the thread page
