What could be wrong if I have went through 1 battery per 1.5 yrs in my 2003 Denali and diagnostics say that my alternator is fine?
Depends, u may do a lot of short runs which dont charge the battery up, u may live in a cold area which hurts the cells or you may be putting the wrong battery or a low quality battery in, some cheaper batteries only last around 2 years. Alarms can cause problems for sure if its not a factory fitted one and drain the battery or something is wired wrong or shorting taking charge from it when the car is off.
Search GMC Yukon Questions
GMC Yukon Experts