When you turn the ignition off, lock the doors, the battery is still working, feeds are still being supplied to stuff, so over time it will probably take out the battery.
A battery removed or disconnected will still lose charge too, but at a much slower rate, so giving it a charge every few months is a good idea, a job for a friend.
Personally, I would leave the battery connected, buy a milliamp trickle charger and leave it connected to the battery.
My fun ride spent most of its life in the garage connected to a milliamp trickle charger for months at a time over many years, always had a fully charged battery to turn the 7 litres of engine...????