03 pete. 379 C15 10 speed old werner truck. Turn all power off on truck when parked a few days and batterirs are almost dead wont turn over . Bit if i hook my ford up ti it it starts right off the bat. Any ideas would be appretiated.
Could be a weak battery pulling them down. How old are the batteries? I doubt it’s a diode on alternator, usually it won’t take 3 days.