Thread: Help! Dual Battery System

Mate has a dual battery system connected in his newly acquired second-hand vehicle. It appears to be a Redarc system. It has a pair of leads, which, when connected, cause a loud click (relay) and a red light to illuminate on the side of the relay system.The relay system is on a connecting lead bridging the two batteries' positive terminals. He assumed this was a means of connecting the second battery to the first for starting purposes if the first was flat. Today he left his lights on and flattened his main battery, so connected the lead and started the car. But when he disconnected the leads, the red light stayed on. He expected it to go off, because the power should be preferentially going to the main battery and the second should not begin charging until the main had lifted. He drove the machine home(about an hour on the freeway), and turned the engine off. The red light was still on. He briefly turned the headlights on and off again, but the red light stayed on. He said he would normally put the main battery on a charger on the basis that an hour's run home would not be enough to bring a completely flat battery up to full voltage again. He measured the voltage and got 13.6 on both batteries.
Should he put the charger on the main battery overnight, or not? Is the system behaving as it should?

Coop

Just spoke to my mate who said he'd gone ahead with the charger overnight and found the light had come back on in the morning, meaning the charger was then charging both batteries. The charger indicated complete charge about an hour later, so all good.
Thanks for the help folks, we both now have a better understanding of these systems.
Cheers
Coop