Thanks - i always knew i was a special person!!
There is no battery in them, the ignition charges the key. There is a possibility of getting the key recoded, if not then you will have to get a new key.
Accprding to Autodata there are 2 types of keys for E46 BMW,on one the batteries CAN be replaced,a little plastic section on the rear of key holds 2 batteries.
for the other key it says -No battery replacement nessessary use each key once a year to recharge batteries.
hi there monkeyboy
this is fairly easily done...the key DOES have a battery, it just recharges from the ignition but eventually it wont hold a charge and will need replacing.
the link bellow shows how its done