Dennis,
I'd like to add to what Hotrod said. Take a small 10-15 amp home battery charger and two batteries. One is perfectly good but discharged and one "sulfated" battery. The good battery will take overnight to recharge("0" reading on gauge). The bad battery may show a full charge in a couple of hours or less. I.E., the more you put in the more you get out.
In your case, you said you noticed a change in the last couple of days, but yet the ammeter returns to "0" as before. In most cases with a "sulfated" battery the ammeter can't return to "0", because the battery can't stay above the constant drain and the alternator is always charging it.
This is why I prefer a ammeter in a car as opposed to a volt meter. The volt meter will generally have the same reading regardless of which of the two batteries I mentioned above are in the car.
Back to your problem. I'd check the charge voltage at the battery. It should be 14v plus. Also check the voltage from batt post(post not cable end) to ground and also to engine block. Should be "0" or a few tenths above. Positive batt post to alternator output post. Should also be only a few tenths. Anything above .5 volts is a voltage drop that you should try to locate and clean up.
