Is there a warning sign on the dashboard to notify you that your car key battery to unlock the doors is running low?

I'm terrified one day I'll be in the middle of nowhere and the battery has run out and I won't be able to get into my car! Surely there'd be some kind of low battery warning?

And where would I get a replacement (lithium?) battery from?

One does exist and if it does run out, it has a key inside the fob, sounds like you're describing keyless entry. 

 

The batteries can be found online easily, had two for a £1 with free delivery not long back, halfrauds wanted a £5 for 1. 

So there'd be a warning when I start up the car to say I need to change the battery? And yes keyless entry, I tried to unlock it the old fashioned way by turning the key in the lock but it didn't work.

I also read at every service if you do it with a dealer or garage they should change the battery as standard. I bought it 6 months ago from a dealership who did give it a service but I have no idea of knowing if they changed the battery or not.

It does warn you when you start the car, that's a bit odd and worth raising with the dealership. 

 

That's interesting, never knew that, do you have a link as I don't think mines ever been changed until I did it. 

A warning I can live with, its just the not knowing and sudden dying of the battery! Well I say dealership it was a used car dealer/garage type thingy. When the guy sold it to me he only gave me a month's warranty.

I think I may have read it on another forum lol.

Most recent models do give battery notifications.
Keyless entry back up blades should work just fine, does yours fit the lock ok?
The battety is a CR2032 and is readily available and easy to swap over in less than a minute, just follow the instructions in the handbook.
If no handbook then you can access the relevant one online here-

https://secure.ford.co.uk/OwnerServices/Owners-Manual

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Its a 2007 model so not sure if its "recent" enough.

By back up blades does this mean to another entry underneath the actual handle? The actual key fits the lock but not sure about any blades.

I have a spare key which I tried on the locks but it doesn't work so maybe the battery in that one is dead. Had to use a phillips screwdriver to prise it open.

The battery won't affect manual locking at all, maybe the actual lock barrel mechanism is duff.

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Hmm possibly, it should in theory still work with the key into the lock. Might be linked with the back driver side door not unlocking/locking properly, the handle just gets stuck.