Any battery 525 Cold Cranking Amps or more is OK for the 390's. Battery size is not the problem since your current battery will crank the enine. When the engine is running right it will fire & start in 2-3 seconds. Since you need a jumpstart to fire the engine , your starting system needs maintenance. 1st the cheap fixes:Get all battery ,cable (both ends), solonoid and starter connections squeakey clean. Check the cable from the solonoid to starter for broken/missing insulation that allows the cable to bleed 12v power ( called AMPS or Amperes) to car body. Worn/burnt insulation in the starter will drain AMPS requiring supplemental power from a jumper battery. Never crank engine more than 15 seconds at a time. The starter will overheat and burn the insulation off the wires inside the starter. When the starter is fried internally, you need a new/rebuilt starter. Also, the cable from the starter solonoid to the starter will overheat and ruin it's ability to conduct Amps to the starter. Had a car once where the cable was burned into 2 pieces ! Need to keep the engine running/starting right to keep the cranking heat to a minimum.
[ 08-08-2002: Message edited by: t-bird-art ]
