1 hour, you need 2 isolated batteries on their own charging circuit
you probably need a second alternator or those batteries won't get fully charged
and a 250W PSU is likely all noy uneed. See: DS-ATX.
Your A64 at stock will pull 80w at full load, 30 to the motherboard and ram, 10 to wireless card, 30 to HD, 20 to DVD, 10 to each LCD = 220w.
Perhaps put the LCDs on their own regulation.