To drain the battery in a couple of hours would have to be a pretty big draw. From your description it sounds more like you have a charging system problem. If I'm right, you can use a portable charger to fully charge the battery in two or three hours, at a slow rate, when you get home at night, and it will still be charged the next morning. If that works, suspect the generator. Start by measuring the battery voltage with the engine running. It must be between 13.75 and 14.75 volts. If it is low, that definitely is the problem. If it is okay, you need to have the second half of the test done with a professional load tester to measure full-load output current and "ripple" voltage. When a generator has one failed diode of the six, you will lose exactly two thirds of the generator's output capacity. 30 amps from the common 90 amp generator is not enough to run the entire electrical system under all conditions and keep the battery charged. The battery will have to make up the difference until it slowly runs down over hours or days.
Most battery warning lights and gauges respond to system voltage, and that will be okay at first when the generator has a bad diode. Many systems only turn the light on when there's no charge from the generator, not for low charge.
Wednesday, February 12th, 2014 AT 8:28 PM