Had a similar problem. It would charge, but take less than a week to nearly die if I took it off and forgot to put it back on charge. I swapped to a lithium one now, find them better. I have a detached single skin garage so it's pretty damn terrible in winter. Poor bike didn't like it.
My 916 would eat batteries like smarties if I let it. Some bikes are just bastards. Despite my 916 being wrapped in a lovely warm blanket and a proper cover. Only the optimate has halted the 916's battery consumption habit. She also chews thru reg/rects. But they're her only foible.
A 17 plate Ducati Scrambler and a 2012 Triumph Tiger , not too much electronics on either , no alarm fitted .
Only thing I leave on pretty permanently is the car on a maintainer. Bikes stay off. If I have not used a while, I put on every now and then and make sure it’s on a day before I use it. But no trackers or alarms to draw power.
