Battery

Just a guess, but I bet it's under the back seat or in the trunk. You can find the owners manual online for free, here: http://bit.ly/BMW_Owners_Manuals

under the back seat passenger side. its real easy to pop the seat but if its never been done before you may need a freinds help

underneath the backseat on the passenger side

it is in the boot on the right hand side

cant send you a diagram but the battery is in the trunk on the right

it is under the back seat