Batteryless alternators are designed to be used on vehicle refrigeration units that require constant maximum output to keep their evaporator and condenser motor running. They are not designed for any battery type application and should not be used with batteries.
When a Batteryless Alternator is turned on it provides the set-point voltage (i.e.: 28 volts) at a constant output (i.e.: 150amps) for a fixed load requirement. There is typically a ‘Bleeding Resistor’ incorporated into the circuit to maintain a constant load in the event the evaporator or condenser motor draw was to fluctuate.
A battery type alternator adjusts its output to coincide with the load requirement which is a combination of running the various items hooked up to it as well as maintaining the charge in the batteries. If there is nothing turned on and the batteries are fully charged, there should be virtually no output.
If you were to use a ‘Batteryless Alternator’ in an application with batteries and there was no load to offset and balance the output of the alternator, it would continue to increase voltage as high as 68 volts. This would literally cook the batteries and could cause an EXPLOSION! Therefore, NEVER use a ‘Batteryless Alternator’ with batteries!