These are smart chargers, so if your batteries are down below a certain level, they may not charge. Since they are internal, and used in garages and homes they have some fail safe features to prevent issues.Try bouncing the battery with a manual charger and then reconnecting the Pro Pack III to see if it functions. The present train of thought at BCB Is more towards three banks with a second support charger for the cranking battery as a stand alone. They use a similar system in the Vision Group models and it has been a pretty reliable and sensible setup. BCB