Standing vehicle guide
Flat Battery After the Car Has Been Standing
About 5 minutes to read
A car left standing loses charge in two ways at once. The battery self discharges slowly on its own, and the vehicle's own electronics keep drawing a small standby current the whole time. Add a cold snap and the same battery that started the car easily in March may not turn it over in November.
There is also a second problem specific to standing cars. A battery that has sat deeply discharged for weeks becomes sulphated, and that loss of capacity is often permanent. That is why a car recovered from a long park frequently starts on a boost, then refuses again a few days later.
Bringing a standing car back
1Check the obvious drains before you touch the battery
Interior lights, a boot lamp, a glovebox light, a dash camera in parking mode or an aftermarket tracker. Any of those turns a long park into a guaranteed flat battery.
2Inspect the battery physically
Bulging sides, a cracked case, weeping around the posts or ice inside a translucent case all mean do not jump start it. A frozen battery in particular must be allowed to thaw and then be tested, not boosted.
3Clean and tighten the connections
Standing cars grow corrosion. Disconnect the negative first, clean both posts and clamps back to bright metal, refit tight, and only then try again. This alone starts a fair share of the cars we see.
4Prefer a proper charge over a jump start
If time allows, a smart charger overnight is far kinder and far more likely to hold than a boost and a drive. A boost gets you moving, but it does not refill a deeply discharged battery.
5If you do boost it, drive properly afterwards
Twenty five to forty minutes of real driving with the heavy consumers off, not five minutes of idling on the drive. Idling barely charges at all.
6Check the rest of the car while you are there
Tyres lose pressure while parked, brake discs surface rust, and fluid levels are worth a look. A car coming out of a long standing period deserves a walk round before a motorway journey.
7Then decide whether it will hold
Have the battery load tested once it is charged. If cold cranking amps are well below the label figure, it has been damaged by the standing and it will strand you again.
How long standing is too long
Rough guide for a healthy battery in a car with normal standby draw.
| What you see or hear | What it means | What to do |
|---|---|---|
| Up to two weeks | Normally starts without help | Drive it properly once it is running |
| Three to six weeks | May crank slowly, especially in winter | Charge rather than boost if you can, then load test |
| Two months or more | Likely deeply discharged and possibly sulphated | Charge slowly, then test. Expect a replacement may be needed |
| Any period with an accessory drawing current | Discharge far faster than self discharge alone | Find and isolate the accessory, then charge and test |
Avoid these with a standing car
- Do not jump start a battery that is frozen, bulged or leaking.
- Do not repeatedly crank a deeply flat battery. You are damaging it and the starter.
- Do not assume a successful start means it recovered. Test it under load.
- Do not leave the car standing again straight away on a battery that only just managed it.
- Do not disconnect a battery on a car that needs codes or settings without knowing what will be lost.
Cars stored, seasonal vehicles and second cars
We deal with standing vehicles constantly, from second cars and classics to vans that sit at a depot between contracts. We arrive with professional boosters, test the battery properly once it is running, and can supply and fit a replacement on site where the standing has finished it off.
Would rather someone came out and did it?
24 hour mobile jumpstart across the West Midlands, with battery testing and replacement on the spot.
Questions
Q.How often should I start a car that is parked up?
A brief start does more harm than good. If you can, drive it for half an hour every couple of weeks, or leave a smart charger connected instead.
Q.Is disconnecting the battery a good idea for long storage?
It stops the standby drain, but it does not stop self discharge, and on some cars you lose stored settings. A smart maintenance charger is generally the better answer.
Q.The car started after standing but died again two days later, why?
The boost gave it surface charge only, and the underlying capacity has gone. That pattern almost always ends in a replacement battery.
In short
Check for drains, inspect the battery, clean the terminals, then charge rather than boost if you have the time. Anything standing beyond a couple of months usually needs testing afterwards. Ring 07886 626640 if you would rather we came out to it.