so both of my key fobs were not working in my 2005 cooper, (three button rechargeable keys), tried reprogramming them with no luck so i decided to open them up to swap out the batteries and to my discovery i find that the two small solder joints on the positive side of the batteries were not even touching, so i pushed em together and went to test the keys and WALA! they work, sealed em back up and now they both work perfect, if anyone else is having this issue, i suggest opening them up and checking to see if the battery is making contact, mine sure wasn't thanks to the two small dot soldering joints that just separated from the battery, to fix this i bent the one metal part facing the positive side so that when i put the key back together it presses against the battery to make a nice connection, So far i have them both sealed back up and there working as they should Hope this helps!

 

how did you reseal it? what did u use