Or buy a battery charger. 

Hi all

I have a 2015 ford fiesta with start stop

The car will start drive then sometimes won’t start without a battery pack

I’ve changed the battery and also the switch on the pedal but it keeps doing it.

Any ideas what it could be thanks in advance

Well, the battery could be duff or low on charge. It could also be due to a corroded battery terminal. You will be applying your jump pack to the OUTSIDE of the terminals. If the inside,, where the battery normally connects is dirty or loose you won't get the current to flow although the dash might light up

Hi anon

Checked everything took the car to Halfords they said everything is ok battery charging alternator fine etc etc

I even had the alarm disconnected and the insurance black box disconnected just in case that was the problem.

I don’t even use the heated seats, radio, etc etc

I was reaching out to see if anyone else has had a similar problem

Halfords only know how to empty your pockets. I very much doubt if they could analyse the complicated charging systems of a modern car but if you have a battery in good order and it is charging properly then it will be perfectly all right to use any of the accessories. If you are covering a decent mileage frequently to charge it up then either there is a drain on the battery (Have you left the boot light on for example,) or there is possibly a failure in the starter solenoid or the starter motor or the wiring to it. Cheap and easy tests that you can do yourself are to make sure that all the wires going to the starter motor are clean, not corroded and firmly attached and that the earth from the engine to the body is sound. Don't just renew bits at random but if those things check out, then reckon that an eleven year old starter motor has probably done its bit and find out if you can get a reconditioned one. I would remove and strip down the old one before I did to inspect it but I cannot assume that you have the time, tools or skills to do so and in that case, I would show this posting to a professional in a local garage and see if their second opinion matches mine.

Hi anon

Thanks gain for your fast response I was definitely thinking there is a drain somewhere so will check what you just said first before proceeding down the starter motor route as It’s such a random thing that only does it every few days I.e

I can come out and start the car leave it running for a few minutes then come back in.

1 hour later come back out and unlock the car go to start it and nothing so put the pack on it and boom starts instantly

It is the random nature of it that points to the starter. f you can start it, run it and all is well but it will not start an hour later without some encouragement, that pretty well rules out a current drain but certainly indicates a failing starter motor. Dirty solenoid contacts would give this fault profile.

39 minutes ago, Gary loomes said:

I can come out and start the car leave it running for a few minutes then come back in.

1 hour later come back out and unlock the car go to start it and nothing so put the pack on it and boom starts instantly

What's the reason for doing that? Only running for a few minutes takes more out of the battery than it puts back in. If the battery was already low, for example after 2 or 3 days without use, then starting and running for just a few minutes will finish it off.

I had similar intermittent symptoms on a Cavalier many years back. Giving the car a jolt (physically or electrically) usually got it going. Corrosion on starter/solenoid terminals was the issue.