I came across this thread: I too am burning through batteries all of a sudden.
I have four hose timers, and all of them had to have new batteries in the past month. That was the original set from last year (everything removed for the freeze, batteries removed, bagged up together, etc.).
Right now, three of them are critical and on the last tick of dying, and they went downhill very quickly. The fourth is hanging in there - no idea why. All four were replenished from the same shipment of batteries. All four are the same distance from the hub. All four pass through the same number of exterior walls, etc.All four run on the same type schedules, water for similar duration, etc.
There was a recent firmware upgrade. Any chance the timers are all 60 times as chatty, or something else along the same lines? At this rate, we could be spending more for the batteries than the timer in rather short order! 
That might make a lot of sense if Rachio had proprietary batteries maybe, but not when you’re just picking them up at the store. 
