Yes, you can measure it yourself. Car makers do not publish a parked-drain figure you can rely on for your model, but your own readings can produce one: note the battery percentage when you park, leave the car unplugged and alone, and read it again before you drive. Two or three similar nights give you a personal baseline — and a sudden change from that baseline is worth more than the number itself.
Key Takeaways
- Makers publish no universal parked-drain figure; measure your own car instead.
- Use the percentage gauge, similar nights, and as few app checks as possible.
- Average three nights to get a baseline you can trust.
- A sudden change from your baseline matters more than the number itself.
Why a Single Reading Misleads
The percentage on the screen is an estimate, not a fuel gauge, and several things move it without any energy leaving the car. Our explainer on whether an EV battery drains when parked covers where the energy actually goes; this article is about measuring your own car.
- Read the percentage, not the miles. The range figure is a forecast that swings with temperature and recent driving. The percentage moves far less for display reasons.
- Expect temperature to bend the result. A cold night can make the same charge read lower, and a warmer morning can hand some of it back.
- Know that looking wakes the car. Every app refresh starts systems that take time to fall asleep again, so checking hourly measures your checking as much as the car.
The Three-Night Test
Run the test on ordinary nights, with the car parked where it normally sleeps:
- Park in the evening with a comfortable charge — mid-range is fine — and leave the car unplugged.
- Note three things in your phone: the percentage, the time, and the weather.
- Leave your features as you normally have them, and do not open the app until morning.
- Before you drive anywhere, note the percentage again. The difference is one night’s loss.
- Repeat on two more similar nights and average the three results.
- Optional second run: switch off security or cabin-climate features and repeat, to see what those features cost you per night.
That average is your car’s parked loss under your conditions — the only version of the figure that was ever going to match your driveway.
What Skews the Result
| Skew | What to do about it |
|---|---|
| A colder or hotter night than usual | Compare like with like; repeat the test in similar weather |
| Frequent app checks | Read the percentage once when you park and once before you drive |
| Security or climate features left on | Run one test night with them off to price what they cost |
| A test of only a few hours | Measure whole nights; small losses vanish inside short windows |
| A weak 12-volt battery | The car may not wake at all — see our guide to whether charging an EV charges the 12V battery |
What Your Number Can Tell You
A small, steady loss that matches your baseline is standby behaviour, not a fault. The result that deserves action is a change: a loss that suddenly grows, a car that will not wake, or a percentage that collapses between two similar nights. Those point to the 12-volt battery or a battery problem, and a battery health check is the next step. The test measures behaviour while parked; it cannot judge battery health on its own.
If the Loss Bothers You, Park Plugged In
If your baseline loss is larger than you like, the practical answer is the one makers suggest: leave the car connected with a moderate charge limit, so standby spending comes from the wall instead of the pack. A wall charger such as the EVDANCE EV-ACT5006T 48A Level 2 wall charger holds that arrangement unattended, and a portable unit such as the EVDANCE EV-ACS3210T 32A NACS portable charger does the same job at a second home. The connected-at-home question is covered in our guide to leaving a Level 1 charger plugged in.
Frequently Asked Questions
How much charge loss is normal overnight?
There is no universal figure: it depends on the car, the features left on and the weather. Your own baseline, and any change from it, is the useful signal.
Does checking the app really use charge?
Yes, a little each time. A refresh wakes systems that then take time to sleep again. During a test, check once when you park and once before you drive.
My percentage went up overnight. Is something wrong?
No. The displayed percentage is an estimate the car revises as conditions change, and a warmer morning can revise it upwards. It is one more reason to average several nights instead of trusting a single reading.
Related Reading
- Does an EV Battery Drain When Parked?
- Does Charging an EV Charge the 12V Battery?
- How to Check EV Battery Health
- Can I Leave a Level 1 Charger Plugged In All the Time?
