GMC Repair: gmc envoy loses battery power every night, gmc dealer, gmc envoy

Question
I have agmc envoy 2002 and had the battery replaced and since then over night the battery loses power every night.I had a gmc dealer look at it,and cost me in excess of $450 but could not identify the loss of power every night.Once boosted in the morning it usually last through the day.I think there is a short circuit some where.please help me to find the problem.thanks

Answer
could be short or a module not turning off, 1st suspect would be if you have onstar, we have seen a lot of those modules not turn off.  Other than that it would be a matter of monitoring the voltage and seeing when it returns to normal by unplugging one module at a time throughout the entire car