Symptom
The vehicle will not start after standing, indicating something drawing current with the ignition off. A welded fuel pump relay is one cause worth knowing about, since it also leaves the pump pressurised.
Also described as: flat battery, battery drain, parasitic drain, battery dies overnight, won't start in the morning, battery going dead, باتری صبح خالی است, باتری شبانه خالی میشود, باتری دشارژ میشود, bateria se descarga noche, amanece sin bateria, bateria se descarga sola, se queda sin bateria cada noche, البطارية تفضى كل يوم, البطارية تفضى لوحدها, البطارية تفرغ بالليل, أصبح عليها فاضية, البطارية تنفد وهي واقفة
3 of the 337 codes that produce this symptom indicate a fault where continuing to drive risks damage or is unsafe. If the symptom is sudden or severe, treat it as one of those until a scan says otherwise.
Three different faults arrive wearing this one complaint: something is drawing current while the car sleeps, the battery no longer holds what it is given, or the charging system never puts back what the journey took out. The arithmetic separates them before a meter comes out of the drawer, and it is the step almost everybody skips.
A healthy 60 Ah battery has roughly 30 Ah of usable capacity before it stops turning an engine. A quiescent draw inside specification — call it 30 mA — takes about six weeks to eat that. A 300 mA drain takes about four days. Flattening a healthy battery in a single night takes something in the order of amps, not milliamps, which in practice means a lamp still lit, a motor still energised or a relay stuck closed. So the driver's own timescale is diagnostic: literally overnight points at a large and findable consumer, flat after standing a week points at a small one, and flat overnight with a draw that measures normal means the battery, not a drain.
What counts as normal is well agreed and not perfectly agreed. German trade press puts a sleeping modern car at 15 to 40 mA; the German technical references say 50 mA maximum and to look up the manufacturer's own figure first; French, Dutch and Japanese workshop sources all land on 20 to 50 mA; Russian references allow 15 to 75 mA and call anything above 300 mA critical. Where they genuinely disagree is the ceiling on a recent car — some German workshop material accepts up to 80 mA on a vehicle carrying telematics and several gateways, while others treat anything past 50 mA as a fault to be explained. Treat the manufacturer's figure as the only one that settles it, and treat 50 to 100 mA as a number you have to justify rather than one you can wave through.
Control units do not go to sleep together; they stagger, and the published waiting times disagree for the same reason. Ten to thirty minutes is what the German trade press quotes, up to thirty in the technical references, thirty in Japanese workshop guidance, forty-five to sixty for full rest in some German workshop material. The disagreement stops mattering if you watch the current instead of the clock — it steps down as each module drops out, and the reading only means anything once it has stopped stepping. What does matter is that anything waking the bus restarts the wait: opening a door, unlocking, pulling a fuse, and on many cars simply leaving the key fob within range of the vehicle. Japanese guidance is the most explicit about the last one and recommends putting the key out of range or in a shielded bag.
That is also why the measurement method matters more than the meter. In series on the negative side, starting on the 10 or 20 A range because several amps can still be flowing before things settle and the milliamp range's fuse will not survive it. A clamp meter with milliamp resolution never breaks the circuit and so never resets the wait. Measuring millivolt drop across each fuse is the method that leaves the car asleep — the current is read off the fuse's own resistance — where pulling fuses one at a time wakes everything and is the slowest way there is on a modern vehicle.
Two branches have no drain in them at all. A battery that has lost capacity to sulphation from short journeys reads a plausible voltage and still will not crank, so open-circuit voltage never condemns or clears a battery on its own — a conductance test against the rating on the label does. And on anything with battery energy management, a replacement battery that was never registered leaves the car charging to the profile of the battery it thinks is still fitted, which undercharges the new one until it sulphates too. That fault presents exactly as "the new battery has gone flat as well", and it is the reason that sentence should never be taken as evidence the first diagnosis was wrong.
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Draw stays in whole amps and never steps down | Something still energised — a boot, glovebox or vanity lamp, a cooling fan run-on, or a relay stuck closed | Read the current: amps rather than milliamps. Find the circuit by millivolt drop across each fuse rather than by pulling them, then isolate the consumer to confirm. | Replace the failed switch or relay. A welded fuel pump relay also leaves the pump live and the rail pressurised — treat that one as urgent rather than as an inconvenience. |
| Steady 100 to 500 mA on a car carrying aftermarket electronics | A hardwired dashcam, tracker, alarm or amplifier on permanent live that never enters standby | Unplug the accessory's permanent-live feed and measure again. Ask what has been fitted before measuring anything — this is the single commonest finding in workshop sources in every language surveyed. | Move the feed to a switched supply, or fit the accessory's own low-voltage cut-out and set it to the battery type. |
| Draw stays high however long you wait, with no step down | A control unit held awake — a door, bonnet or boot latch switch reading closed, or a module that will not sleep | Compare the body or gateway module's live door and latch states against the doors' real positions, and watch which fuse's current fails to fall. Check no key fob is within range of the car. | Replace the failed latch microswitch, or repair the module that will not sleep. Do not fit a battery for this fault. |
| Draw falls to normal the moment the alternator's B+ lead is disconnected | Leaking rectifier diodes letting current run back into the alternator with the engine stopped | More than about 60 mA measured at the disconnected B+ terminal is the figure the references use. With the engine running and loaded, more than roughly 0.5 V AC at B+ points the same way. | Replace the rectifier pack or the alternator. A diode can test healthy cold and leak once the engine bay is hot, so measure warm if the cold test is clean. |
| Draw settles inside specification but the car still will not crank after one night | The battery rather than a drain — usable capacity has collapsed, so an entirely normal overnight draw is enough to finish it | Charge fully, rest four hours or more off charge, then read open-circuit voltage (12.6 to 12.7 V healthy, under 12.4 V needs charging) and follow it with a conductance or CCA test against the label rating. | Replace with the correct type and capacity — AGM for AGM — and register or code it where the car has battery energy management. |
| A recently fitted battery has gone flat as quickly as the one it replaced | The replacement was never registered, so energy management still charges to the old battery's ageing profile and undercharges the new one into sulphation | Read the battery data stored in the energy-management module and compare it with the battery actually fitted, then check charging voltage at the terminals under load against the manufacturer's figure. | Register the battery — type, capacity and serial — with the manufacturer's tool or an equivalent. Check too that AGM has not been replaced with flooded. |
| Flat after several days rather than one night, on a car that only does short journeys | A charging deficit: the battery never returns to full, and the sulphation that follows takes capacity permanently | Rest voltage below 12.4 V despite recent driving. Compare charging voltage at the battery against the manufacturer's figure, and on a start-stop car read the battery sensor's own state-of-charge rather than trusting a voltmeter. | Recharge properly off the vehicle with a modern charger, then change the use pattern or fit a maintenance charger. Replace if the conductance test has already fallen away. |
| Draw is normal, the battery tests good, and the car stands for weeks at a time | Nothing is wrong — a legitimate quiescent draw plus self-discharge, over a standing time longer than the battery was ever going to cover | Do the arithmetic rather than the diagnosis: usable capacity in amp-hours divided by measured draw in amps gives the hours to flat. Compare that with how long the car actually stands. | Fit a maintenance charger or a battery isolator. Do not chase a drain that is inside specification — there is nothing at the end of it. |
Draw stays in whole amps and never steps down
Steady 100 to 500 mA on a car carrying aftermarket electronics
Draw stays high however long you wait, with no step down
Draw falls to normal the moment the alternator's B+ lead is disconnected
Draw settles inside specification but the car still will not crank after one night
A recently fitted battery has gone flat as quickly as the one it replaced
Flat after several days rather than one night, on a car that only does short journeys
Draw is normal, the battery tests good, and the car stands for weeks at a time
Listed with the codes that most typically present this way first — the likeliest place to start.
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
A parasitic drain is current the car draws while it is switched off and locked. Every modern car has some — the ECU, the clock, the radio presets and the alarm all keep their memor...
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