Second battery is worthless too. Batteries are 12v. Usually the car's electrical system is above that. So, the battery won't do anything until the alternator is strained and the system's voltage drops to 12v. Then the batteries will keep it from dropping any lower until they are dead. Only problem is that when the load lifts now the batteries are drawing current as they try to recharge.

The only real answer to the problem is a better alternator.