Ford Repair: Dead battery, alternater, battrey

Question
I have a 2000 ford explorer. Last february the battery would occasionaly die, Sears told me it was bad and replaced it with a new one. A month later I had the same problem. I thought one of my kids left the lights on thus draining the battery. A month after that it failed again I brought it to a shop they tested the alternater, said the test equipment showed a bad diode. They replaced the alternater. Two days later I had the same problem - dead battrey. I brought it back to the same shop, they found nothing wrong. In the last three days I measured the voltage accross the battery Friday 12.8 volts , Saturday 9.3 volts, Sunday 7.8 volts, today 5.8. During this time I have had a battery charger on it ofr 1 - 3 hours at various times. I have had it suggested that the starter is hung up and thus drawing the battery down, a suggestion there is a short in the wiring or the new battery is bad. Do you have any thoughts before I poor more money into this?  

Answer
If you are charging the battery and it still goes dead, you have either a bad battery or in your case more likely would be a short to ground or heavy load drawing down the battery. A competent shop should be able to track this problem down with a meter hooked up to check for a large draw. Typically .5 volts or higher on this test is the limit we look for as far as battery-killing. You may have a relay sticking or something like that. If you can leave it with a shop overnight and have them monitor the battery drain overnight or all day. These problems can be intermittent, in most cases a short of this kind will drain a battery overnight.

A hung up starter will not start the engine, and if it does hang it will keep spinning so it would be obvious. EVERYONE will offer you an opinion as to what the problem is, you need some one who can FIND the problem.