Hello all, not tried the 'spare' but key that I have had since got car gave up ghost....managed to lock it but it did not unlock with key fob...had to manulaly unlock then manually lock....stuck key in fridge and after 10mins tried again and key works..so battery? how feasible is it to replace the battery? tad worried about taking knife to it as did this on wifes e46 key and destroyed it a while back....plus what battery is needed?any ideas much appreciated

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E53 X5 3.0d SUV prod.date 11/2004 eng.variant M57N Europe Right hand drive N