We keep batteries in all of our devices and do not get leaks. We have found that if you put a bit of insulation [like paper or a bit of plastic bag] on the end of the battery that is exposed when you open things up they stay fresh. We do not do this with 9V batteries but it has worked for us for several years.
I suspect there is some sort of microvoltage leak which discharges batteries and makes them more vulnerable to corrosion if they are not insulated.