her focus mk2.5 remote is getting decrepit at 160k miles (I want to retire it, as a just about functioning spare and start again), so I bought a nasty blank for a fiver and second-hand remote for another fiver - the plan to break things and cry

In the mean time threw a brand new battery in the remote that needs coding (3.08v out and 3.35v going in). 

Measured her current battery which i replaced a year back with a new Duracell one - but it never helped - it was just as useless and obstinate operating the locking as it was on the old flat one.  Her current key's battery is at 3.09v is this supposed to be sufficient for normal operation?

Battery new out of the box should punch out 3.3v, I've found that once it deteriorates to 2.9v, it causes issues. No idea if that helps or not 😂

17 minutes ago, StephenFord said:

Battery new out of the box should punch out 3.3v, I've found that once it deteriorates to 2.9v, it causes issues.

I've found similar. A new cell shows 3.3v, I've replaced 3 batteries so far in the fobs of my present car when "key battery low" came up.on the dash display and they were at 2.8v.

(Plus one which must have been a dud - it showed 3.3v out of the pack but 2 days later wouldn't open the car and was "not detected" - when I took it out and replaced it I found it had dropped to 1.9v.)

I agree with all the above. I started getting a warning when mine dropped from 3.3 (new) to 3.03, they still worked though but probably for not much longer.

I wouldn't buy Duracell ones again. I replaced one of mine with a Duracell one bought from a well known supermarket and it only lasted a few months. I did remove the sticker.

My wife’s Mazda 2 seems very susceptible to less than perfect remote batteries. They are smaller than Ford batteries. I bought an Energiser battery which has been fine.   But with all top brands some will be fake you just have to hope that national chain shops check they only buy genuine

thanks - yep I thought her's has enough to do the business - strange the old original behaved a bit yesterday - seems temperamental - but I expect it just thugs hacking signals

having attempted to follow the lunatics advice on the remote on youtube - I found a load of lies and misinformation - then a polish one with subtitles that is correct for BOTH bits

its even in the handbook - clearly written how to programme any (correct ford) key to your car for door locking - the 4 quid one now does her door lock as well as the original - you set the car up with 4 on off cycles then click any remote at hand and they become door locking keys for your car

the next bit is the immobiliser info and I need to put my license on the laptop for forscan

https://www.youtube.com/watch?v=df9K56YY-Ic