GMC Sierra 2500 HD won't start without battery pack, voltage drops from 13.7 to 4.5 volts on GMC Sierra 2500 HD

Some GMC Sierra 2500 HD owners report experiencing starting issues when the vehicle won't start without a battery pack, with voltage dropping significantly from 13.7 to 4.5 volts. This problem may indicate a faulty battery that is unable to hold a charge or provide sufficient power. Additionally, some owners find that a malfunctioning alternator fails to maintain the battery's charge, contributing to the voltage drop and starting difficulties. Others have reported starter troubles, where a failed starter either does not engage properly or draws too much power, causing further voltage issues. To address these concerns, owners are advised to check the battery's charge, inspect the alternator for proper functioning, and examine the starter for excessive power draw. If these steps do not resolve the issue, consulting a mechanic for a more thorough diagnosis may be necessary.