Seriously, if the battery goes flat after less than 3 months then Morgan has not specified the correct battery to go with the BMW electronics.
It's a little more complex than that Peter. Because of the way Morgan has adapted the BMW CAN bus electronic control systems for the Aeros, there are some circuits which stay 'live' even when the ignition is off. These will place a residual drain on the battery. (Max owners will be aware of the always-on rear glass release light for example).
It's true that the standard-fit Banner batteries are not the best and an Exide Gel battery has made a huge difference. But the best remedies are - as others have posted - to always use a trickle-charger and if this is not possible use the inertia cut-out switch to isolate the electrics.
