What parasitic drain is, in plain terms
When you lock the car, it does not fully switch off. VARTA lists alarms, door locks, keyless-go and navigation systems as items that keep using power while the car is parked. That steady trickle is called parasitic drain or key-off draw. It is normal, but over weeks without driving it adds up, because nothing is putting the charge back.
What is normal car battery drain overnight?
Overnight, a healthy car typically draws a few tens of milliamps, which costs very little charge. OPTIMA treats about 25 mA as acceptable, notes that 85 mA is not unusual on newer cars with more electronics, and says anything over 100 mA points to an electrical fault. Well-equipped cars with many control modules, which includes many recent luxury models, tend to sit at the higher end. A car that is flat after one or two nights has a fault, not normal drain.
| Draw with the car locked | What it usually means |
|---|---|
| Around 25 mA or less | Acceptable on most cars |
| Around 50–85 mA | Common on newer, well-equipped cars; the battery needs regular charging |
| Over 100 mA | Likely fault: a module not sleeping, an aftermarket device or a stuck light |
How long a parked battery lasts
A rough calculation shows why a long trip is risky. At 85 mA, a car uses about 2 amp-hours a day, so a 60 Ah battery loses roughly a quarter of its charge in a week and close to all its usable reserve within a month. The heat makes this worse: VARTA notes that high temperatures increase self-discharge, so a car parked in a hot UAE garage loses charge faster than the same car in a cool climate. Dashcams with parking mode, trackers and other added devices shorten the time further.
This is a worked example, not a promise. A battery that is already old or weak may be too flat to start the car after a much shorter absence.
Why a deep discharge in heat can finish a battery
A lead-acid battery left flat does not just wait to be recharged. OPTIMA says letting voltage drop below about 12.4 V leads to sulphation, where hard crystals form on the plates and reduce capacity. VARTA states that deep discharge can damage a battery irreversibly, and that the lost capacity can at best only partly be recovered with a reconditioning charger. That is why a battery that sat flat for a whole summer often starts the car after a jump but fails again days later.
Your options before you travel
There is no single right answer; it depends on how long you are away and where the car is parked. The table compares the three common choices. Whatever you pick, start with a fully charged battery: VARTA suggests 12.7–12.8 V before storage, and recommends recharging once it reaches 12.5 V or less.
| Option | Works well for | Trade-offs |
|---|---|---|
| Battery maintainer (smart charger) | Trips of a month or more | Needs a socket near the bay, which many residential basements lack; use a charger with a maintenance mode to avoid overcharging |
| Someone drives the car weekly | Most trips, if a friend or relative is available | Needs a proper drive, not a five-minute idle; insurance must cover the driver |
| Disconnect the negative terminal | Older, simpler cars with no maintainer option | Clock, radio and window settings reset; the alarm is off; some cars need relearning or show warnings; the battery still self-discharges |
Will a car battery drain if disconnected? Yes, but slowly: disconnecting stops parasitic drain, yet the battery still self-discharges, and faster in heat. Check the owner’s manual first, loosen the negative terminal only and tuck the cable away from the post.
Hybrids and electric cars left parked
Hybrid and electric cars still rely on a small 12-volt battery to unlock the doors, wake the computers and switch the main system on. That battery faces the same parasitic drain as a petrol car, and on many models it is smaller. When it goes flat, a car with a full main battery can still refuse to power up. Follow the maker’s storage advice for both batteries, and see our guide to hybrid 12V battery replacement if the small battery keeps letting you down.
If the battery keeps draining even after short stops
A battery that goes flat after a weekend, not a month, points to a fault or a worn-out battery rather than normal drain. Common causes are an aftermarket alarm, tracker or dashcam wired permanently live, a boot or glovebox light that stays on, or a control module that does not go to sleep. An old battery that has lost capacity can look like a drain problem too, because it simply holds less. A battery test is the first step, since it shows whether the battery itself is the weak link before anyone starts hunting for a drain.
A checklist for the week before you fly
A few small steps make the biggest difference. Most of them cost nothing.
- Drive the car for a proper run in the days before you leave, so the battery starts full.
- Switch off or unplug dashcams in parking mode and any plug-in accessories.
- Make sure every light, the boot and the glovebox are fully closed.
- If the battery has already been through a couple of UAE summers, have a battery test before you go rather than finding out on return.
- Leave the key with someone you trust if a friend will drive the car, and agree a weekly routine.
- Save the number for a 24/7 jump start in case the car is flat when you land.
If the car is flat when you get back
A jump will often start it, and our guide on how to jump start a car explains the safe clamp order. A battery that has sat flat in summer heat needs checking afterwards, because it may have lost capacity for good. When you call us for a jump start, the technician tests the battery and charging output after the car runs, so you know whether it will hold. If it will not, we offer 24/7 car battery replacement in Dubai, Sharjah and Abu Dhabi, with the battery tested first and fitted where the car is parked. If the car is stuck underground, flat battery in basement parking explains what to share when you call.
| Step | What it does | When it is enough |
|---|---|---|
| Jump start | Gets the engine running | When the battery was simply run down and recharges normally |
| Battery test | Shows whether the battery still holds charge and whether the charging system works | Always worth doing after a summer spent flat |
| Replacement | Fits a new battery matched to the car | When the test shows lost capacity or the car needs jumping again |