albeit a small one, your Security System is a parasitic draw. Ima 68 yr. old goat & don't drive as much as I used to, so I turn mine off in the A.M. & turn it back on after dark. I charge monthly with my Romondes charger. & drive 60-80 mi./week. my batt. is about to turn 3 & everything seems to be o.k. Been a Mini owner since 7/2020 & I'm learning all the quirks.

 

Not sure if the newer minis can do it but the older minis security systems used to turn on only after hitting the lock button on the key twice.

 

I hit the Fob lock button on my '15 F-56 to lock. I hit the Fob open button & inside driver's door I hit the UP button to unlock pass. door, hatch door & gas cap if I hit the fob open button twice it opens all the others. I'm pretty sure that when I hit the Fob Lock Button once it locks everthin & turns the alarm on.