My wife has a 64 plate Fiesta. It's used for short trips around town only, a 1.0 ecoboost.

Yesterday she went to start it and the battery was flat as a pancake. It had been sitting since Friday with no noticeable battery issues. She thinks there was a boot open light showing when she got to the car.

RAC came round yesterday and it started immediately their charger was attached to the battery. I left it running for an hour. Started it again this morning and it was a bit slow to turnover, so obviously hasn't held its charge very well (or something is draining it). She went to start it again this morning (I tested it at 7:30am and it was a bit slow to start) and by 10am it was flat again, and showing the boot open warning.

My question is, should I just go and get the battery replaced, or is there some basic testing I should do first to confirm that the problem is the battery rather than a parasitic draw on the battery when the engine is off?

My initial reaction was to just go and get the battery changed as it's probably either already in need of replacement (5 years old and short journeys only) or it's now reached the end of its life as a consequence of being completely drained. However, I don't want to waste a load of money on the battery only to then have another one go the same way.

Could the boot open warning be the source of the problem? Or more likely a symptom as a result of the battery problem?

Thanks in advance.

Is the boot light on ? 

Yes, so I’m told. I’ve been at work both times the battery has been discovered to be flat.

The light wasn’t on when the battery was charged yesterday and the car was running.

Temporary I would unplug the light then  and see if battery recovers it charge with a bit of a drive. 

If it does then you have issue with the boot light switch( which is part of the boot latch assy) 

If you do decide to get a new battery, make sure you get the right type and size.  Efb 590  (Enhanced flooded battery ) 

Thank you.

Is there a way to test the health of the battery? The RAC man seemed to think that the fact it had been run right down to no charge would mean it would probably need replacing even if previously ok.

 

https://www.kwik-fit.com/batteries/search/details/AFB100E

 

This is the battery that Kwikfit think the car needs. Is this right?

 

Finally, the RAC guy said to leave it running on the drive for an hour last night and that taking it out or just leaving it running didn't make much difference. Is he right? Or should I have taken it out for a bit?

The RAC person should have been able to test voltage and load easily. In my experience they are keen to call out the battery just because they started it, so if they haven't the fault is not there. AA missed my faulty glow plugs (diesel - error code was there for anyone who looked to see) and worn earth strap - on both occasions the fault was much cheaper to resolve than the price of the new batteries I bought on their advise.

Take it for a drive rather than leaving it running on the drive, I would be more inclined to call the RAC back and get them to check the boot light.

"Finally, the RAC guy said to leave it running on the drive for an hour last night and that taking it out or just leaving it running didn't make much difference. Is he right? Or should I have taken it out for a bit?"

in the old days it wouldn't really charge on tickover but modern alternators are much higher output and leaving it on tickover should still be charging it as good as driving it, assuming nothing else is on like lights. Putting a volmeter on it whilst running would be useful to be sure but I know not everyone has a voltmeter.

The best way to check if the battery is really failing or if there is something draining it is to disconnect the battery after charging it and then only reconnect it when you want to see if it starts the car well. Of course if it still seems to have lost a load of charge then it must be the battery and not something draining it.

In my previous Fiesta the battery lasted just over 10 years but it was doing 350 miles per week.

On my current fiesta I kept wondering why stuff in the glovebox was warm. I then i found the glovebox light was permanently on. It may have been on for over a year. To be sure it could not happen again I removed the bulb.

Thank you - that's very helpful.

Is disconnecting a battery something that I can do myself by watching a youtube video without complication and risk of shock?! Surely it must be....

I've a mechanically minded friend that I suspect has a multimeter, I might see if he can help me out in exchange for a couple of beers.

Before doing anything else, I'd take the bulb out of the boot light and see if it makes any difference.