Car Battery Draining Overnight? 11 Real Causes and Fixes
Waking up to a dead car battery? Here are 11 real reasons your car battery drains overnight — and exactly how to find and fix each one without a dealership.
A car battery drains overnight because of parasitic electrical drain (the #1 cause), a failing alternator that stops charging while driving, a battery that is too old to hold charge, or a door/trunk light staying on. The fix starts with a multimeter test: set it to DC amps, disconnect the negative terminal, and measure current draw. Anything over 50 milliamps with the car off means you have a parasitic drain to track down.
