Dont want to waste time or $ on unneeded parts!
Well , if thats the case.....Look elsewhere from Battery Temp sensor. As the name implies, It measures the ambient temperature of the Battery and feeds this information to PCM....where your voltage regulator uses it to protect from overcharging a cold battery. A failure in this sensor would set a DTC and Check engine lamp, and would default to 65 degrees F., which WILL NOT CAUSE A LOSS OF VOLTAGE.
Now.....As I have asked before in other threads.....DO you buy Meat from the plumber??? Does the butcher come over to fix your leaky Toilet? ..Of course not...So why are you letting a salesman fix your car??? Parts stores offer these services to "SELL PARTS", and most of the "SCAN" and "BATTERY" boys are not competent enough to tie their shoes.
Bring the car to a COMPETENT mechanic, and ask for a PARASITIC LOAD TEST. If they dont understand..try again somewhere else.