Battery Keeps Dying: Parasitic Draw, Alternator Failure, and Dead Battery — Complete Fix Guide
Why Your Battery Keeps Dying
A battery that repeatedly goes dead has one of three root causes: a parasitic electrical draw that drains the battery when the car is off, a failing alternator that is not recharging the battery while driving, or a battery that has reached end of life and can no longer hold sufficient charge. The easiest first test: jump start the car and measure alternator output voltage at the battery terminals with the engine running — 13.8 to 14.4 volts is normal charging range. Below 13 volts indicates alternator failure. If the alternator output is normal, perform a parasitic draw test with a multimeter in series with the negative battery cable.
Test Procedure and Repair Cost
Parasitic draw test: disconnect the negative battery cable and put a multimeter set to DC amps in series. Normal standby draw is under 50 milliamps after all modules sleep (10 to 15 minutes). Above 100 milliamps indicates a parasitic draw. Pull fuses one at a time to identify the circuit. Battery replacement: $80 to $200 DIY, $150 to $350 shop. Alternator replacement: $100 to $250 DIY, $350 to $650 shop. Parasitic draw repair varies widely by source — from a $20 relay to $300 for a faulty module.