You parked the car at midnight with 78% battery. You walked out at 7 AM and it was at 73%. Nothing was scheduled. Nobody opened the door. The car sat in the garage the whole time, alone.
So where did the 5% go?
The internet calls this phantom drain (or vampire drain, depending on whom you ask). Everyone has an opinion about it. Some Tesla owners say they lose 1% a night and shrug. Others swear they lose nothing. A few swear they lost 8% on a weekend trip without driving anywhere. Almost nobody can tell you why their number is what it is.
This is a guide to figuring out your own number. And what to do when that number starts saying something is wrong.
What is phantom drain, actually?
A Tesla is never fully off. Even when nobody is around, the car keeps several systems running quietly in the background. The main computer. The body controllers. The cellular modem talking to Tesla. Cabin sensors that watch for motion. Depending on your settings, the cameras, the climate system, the battery's thermal management.
Each of those has an idle power draw. Add them up, throw in the occasional wake event when something needs to do real work, and you get a slow trickle from the big battery to the 12V system.
For a typical Model Y or Model 3 parked overnight in mild weather, here's what looks healthy:
- 0.5% to 1.5% per night is normal.
- 2% to 3% per night is on the high side but not alarming.
- 4% or more per night usually means something is actively burning power.
The annoying part is that "something" can be one of six culprits, and the Tesla app will not tell you which. So let's go through them.
The six things that wake your Tesla at night
1. Sentry Mode
If you leave Sentry on while parked, you are basically running a 4-camera security system 24/7. The math works out to about 250 to 350 Wh per hour. That is roughly 1% of a Long Range battery every two hours.
So a full day of Sentry will cost you 8% to 12%. Most owners only use it in unfamiliar parking lots. But if "Sentry except at home" is on and your car can't geofence "home" correctly, you might wake up to a 5% or 6% loss for no obvious reason.
A quick way to test this: turn Sentry off for three nights. If the loss drops, you found your answer.
2. Cabin Overheat Protection
In hot climates this one is silent and brutal. With Cabin Overheat Protection set to "On", the car runs the A/C if the cabin gets above 40°C, even when nobody's there. A single 90-minute cooldown can burn 3% to 5% of the battery.
If you live somewhere that hits 38°C in July, this can become a 6% to 8% daily loss that you don't see in the trip log. Because it happened while you were at work.
The cost adds up too. A 6% daily phantom drain on a Long Range Model Y is about 4.5 kWh of replacement charging every day. Whether that ends up costing you a little or a lot depends entirely on your charging mix, so we built a charging cost calculator that turns your specific setup into a monthly number.
3. Scheduled climate preheat
If you have a "departure" schedule in the Tesla app (say, "leave at 8:30 AM weekdays, cabin to 22°C"), the car starts preconditioning about 45 minutes before you leave. On a cold morning that means a battery heater and a cabin heater pulling 6 to 8 kW for half an hour. Routine cost: 2% to 4%.
This is a phantom drain you actually wanted. But it's worth knowing about because it makes your morning numbers look worse than your real parked drain.
4. Firmware checks and over-the-air updates
Tesla sends small firmware checks every few hours, and stages OTA updates while you sleep. The check itself is cheap, under 0.1% per cycle. But a pending update that's actually downloading can keep the car awake for half an hour and burn 1% to 2%.
You'll see this as "occasional" higher-loss nights with no other obvious reason. The morning after an OTA usually has a 2% to 3% extra dip compared to a normal night.
5. Cell modem chatter
Your Tesla is in constant, low-bandwidth contact with Tesla's servers. Location, telemetry, diagnostic events. In normal use this costs you a fraction of a percent per day.
But here is where it gets sneaky. In a garage with bad cell reception (basement, thick concrete walls), the modem boosts its transmit power to keep the link alive. That can quadruple the modem's idle draw.
So if your drain is higher at home than at the office, or vice versa, the difference is often just the cell signal strength.
6. Background telemetry from third-party apps
Every Tesla companion app you've ever connected (TezLab, Tessie, A Better Routeplanner, Stats for Tesla, even your dealership's service app) holds an OAuth token that lets it poll your car. Old apps you forgot about can be waking the car every 5 minutes to "check status."
This one is the most underrated culprit. We've actually seen owners discover that a former roommate's app was still polling the car, four years after that person moved out. The fix is a 30-second purge of OAuth tokens in your Tesla account settings. But you have to know to look.
How to investigate yourself
The Tesla mobile app gives you today's battery percentage and not a lot more. To figure out which of the six culprits is yours, you need three things.
First, a consistent baseline. Pick three nights when nothing weird is going on. No Sentry, no schedules, no extreme weather. Record the battery percentage at park time and again at 7 AM. Average them. That is your real overnight drain.
Second, one variable at a time. For the next week, change one thing each night. Sentry on, Sentry off, schedule on, schedule off, Cabin Overheat on, off. Write down each result.
Third, a spreadsheet or a notes app. This is the boring part nobody actually does. Which is also exactly why most people don't know what their phantom drain is.
A week of this gives you the answer. It is also the kind of thing that no smart person on Earth actually wants to do. Which, to be honest, is the whole reason we built Volt. But you can do it yourself.
What's normal versus what's a real problem
Use these as rough goalposts for a Long Range Model Y or Model 3 in mild weather (10 to 25°C), no Sentry, no schedules:
| Overnight loss | What it probably is | | --- | --- | | 0% to 1% | Healthy. Just the modem and 12V system idling. | | 1% to 2% | Normal. Cellular boost or a quick OTA check. | | 2% to 4% | High. Look for Sentry, a forgotten schedule, or app polling. | | 4% to 6% | Something is firing. Audit settings and third-party apps. | | 6%+ | Worth taking seriously. Could be a wake loop, a bad sensor, or in rare cases an actual battery issue. |
Numbers shift up in winter (battery heater) and summer (cabin overheat). A 3% night in minus 10°C weather is fine. A 3% night in an 18°C garage, parked alone, is worth a closer look.
Why the Tesla app won't help with this
The Tesla mobile app is designed to be reassuring, not analytical. It shows you a battery percentage and a range estimate. It does not show you a timeline of when the car was awake versus asleep last night. It does not show you which subsystem was active when it was awake. It does not show you whether there's a third-party token quietly polling your car right now. It does not show you a trend across multiple nights.
This isn't a bug. It's a design choice. Tesla doesn't want the app to be the place where you doomscroll your car's vitals. Fair enough, honestly.
But it does mean that if you actually want to understand what your car is doing while you sleep, you need a second tool.
How Volt handles it
Volt is the companion app we built because we got tired of running that spreadsheet ourselves. The relevant feature here is what we call the Phantom Drain Detective.
It logs every wake-up your car had overnight. When it happened, how long it lasted, and roughly which subsystem caused it. It separates "expected" drain (the Sentry you opted into, the schedules you set) from "background" drain (modem, firmware, third-party polling). It flags any night where the loss falls outside your personal normal range, not some generic threshold.
And then it tells you, in plain language: "Last night you lost 4.2%. Sentry was on from 11:47 PM to 6:12 AM and that accounts for 3.8%. Your baseline drain was 0.4%. Nothing else to worry about."
We're not trying to pitch the app as a solution to a problem you don't have. If your phantom drain is a healthy 1% a night and you don't care, you don't need Volt. But if you've ever stared at your Tesla's battery in the morning and thought "where did that go," that is exactly what we built this for.
What to actually do if your drain is too high
In rough order of how often each one works:
- Audit third-party app tokens. Tesla account, Account, Security, Authorized third-party apps. Revoke anything you don't actively use.
- Turn off Cabin Overheat Protection if you're not in a hot climate. Or at least switch it from "On" to "No A/C".
- Check Sentry's geofencing. "Exclude Home and Work" only works if those addresses are actually set. Otherwise it doesn't.
- Disable scheduled departures you no longer use. A leftover "preheat at 7 AM" from your old commute is a daily 2% to 3% you don't need.
- If drain is persistently 5% or more with all of the above clean, book a service appointment. The 12V battery may be failing (which forces the HV battery to wake repeatedly), or a sensor may be stuck on. Real hardware faults are rare but they happen.
A few questions people always ask
Is phantom drain normal?
Yes. 0.5% to 1.5% overnight is healthy on every modern Tesla. It's the price of being an always-connected car.
Does Tesla cover phantom drain under warranty?
Not by itself. They'll only investigate if it's clearly tied to a hardware failure. 12V battery, sensor, or traction battery degradation.
Does plugging in eliminate phantom drain?
Effectively, yes. The car sips from the wall to maintain battery state, so you see 0% loss overnight even if the underlying systems are still drawing power. The drain isn't gone. You're just paying for it from the wall instead of the battery.
Will closing the Tesla app on my phone help?
A little, but not much. The official Tesla mobile app polls your car relatively rarely. Third-party apps with stale tokens are a much bigger source of wakes.
Is it different in winter?
Yes. In freezing weather the battery heater runs periodically to keep the pack warm, especially if you have a scheduled departure. 3% to 4% on a minus 10°C night is normal.
If you've made it this far, you probably care enough about your Tesla to want answers like these on tap. That is exactly what we are building. Volt is in private beta and we are letting people in slowly. The form on the homepage will keep you in the loop.
Either way, now you know what's eating your battery while you sleep.