Why does my Wagon R battery drain overnight even with a new alternator and battery?

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Why does my Wagon R battery drain overnight even with a new alternator and battery?

I recently installed a new alternator and battery in my 2018 Suzuki Wagon R, but the battery still drains overnight, and I need a jump-start in the morning. A mechanic tested the alternator and said it’s working fine. Could there be an issue with alternator wiring, diodes, o r some kind of electrical short drawing power when the car is off? What should I check next to fix this parasitic drain?

Gari Specialist asked on 24 May 2025 16:33:37 pm

1 Answer

11 views |

Gari Master - on 24 May 2025 16:36:19 pm

If your battery drains overnight despite new alternator and battery, the issue is likely a parasitic drain—some electrical component is drawing power even when the car is off.

Common Causes:

Faulty radio, tracker, o r aftermarket accessories

Alternator diode failure, allowing reverse current flow

Short circuit o r faulty wiring

Faulty ECU o r immobilizer relay

What to Do:

Disconnect the battery negative terminal and connect a multimeter in ampere mode to check if there’s current draw. It should be less than 0.05A.

Start pulling fuses one by one to see which circuit is drawing power.

If draw s when you pull a fuse—that’s the faulty circuit.

Tip: A bad alternator can still pass a voltage test but leak power internally—ask the electrician to test it for reverse drain.