Battery Keeps Dying Overnight
If your battery is consistently fine during the day but dead by morning, something specific is drawing power while the car sits — and it's usually one of a few common culprits.
The usual causes
- An interior light not fully switching off — glovebox, boot, or door courtesy lights are common offenders.
- Aftermarket electronics — dashcams, alarms, or trackers that draw a small but continuous current.
- A faulty relay or module that's staying partially active instead of fully powering down.
- A battery that's already weak, where even the car's normal standby power draw is enough to finish it off overnight.
Finding a parasitic drain
A parasitic drain test measures how much current is flowing from the battery when the car is completely off and locked. Anything more than a very small standby draw (needed for the alarm and computer memory) points to something specific pulling power that shouldn't be.
Fixing it properly
Once we identify whether it's a drain or a genuinely weak battery, we can advise the right fix — whether that's addressing the specific electrical fault or replacing a battery that's simply no longer up to the job.
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Yes, this is part of our diagnostic process when a battery is repeatedly dying overnight.
Not always — if there's a genuine electrical drain, a healthy battery may just need the drain addressed rather than replacing the battery itself.
An older battery has less reserve capacity, so even a normal small standby draw can be enough to flatten it overnight — replacement is usually the right call in that case.