Q: Why won’t my battery hold a charge if it’s new?

The problem you are describing is what we call a parasitic draw on the battery, which is an excessive draw that prematurely kills the battery either over a certain amount of time or overnight. In order to test the system draw, an amp probe on a positive battery cable is used to see if more than 50 milliamps are being drawn.

There are two potential issues which may be killing your battery. The first, the A/C relay may stick closed after shutting off the engine, which would draw excessive amps and cause your battery to die in 8 or more hours. Replace the A/C relay to fix this. The second problem is that the sunroof module is causing excessive draw, killing the battery with in a week or two. Reprogram the roof module at the dealer to correct this. Another problem could be that the body control module is not going to sleep after shut down, which may be due to the door ajar switch or other issues. A thorough diagnostic would be needed to uncover what exactly is keeping the module awake. A trained mechanic, such as one from YourMechanic, can perform a battery inspection to determine why your battery is will not hold its charge at your home or office.