I've had three of these in regular use for years. They're superb value.
With specific regard to using a trickle charger on the Z4M: use the connections under the bonnet. From memory, there's a +ve connection under a black plastic cover on the bulkhead (left side) and -ve connection (exposed nut) on the left suspension tower. Simply connect the clips of the charger to the two terminals and run the wires out through the bonnet when it's shut. They really are idiot-proof!