The standard alternator on the main engine is intended for charging the starter battery. Starting the engine requires a high current, but in a very short time, so that the battery remains nearly fully charged. The starter battery can, therefore, be recharged to its full capacity with a low output alternator and a simple single stage regulator. The charge voltage is in general set at approximately 14 V or 28 V. The service battery, in general, has a much higher capacity and will often be deeply discharged. At the same time, the requirement is to recharge the service battery as fast as possible. This can only be achieved with a high output alternator and increased charge voltage. Under these conditions, an intelligent multi-step regulator will be needed to avoid early failure of the battery bank.