Good point. One should consider to keep the battery on the outside of any machine that is not frequently cared for. Even recent battery makes have a tendency to leak when discharged (nasty corrosive stuff comes out). Simply attach the external battery connector or battery holder to the back panel of the computer (adhesive tape might do). For one machine I cut a piece of plastic into the size of the original PRAM battery and attched a wire to each end, so it serves as a plug to contact the battery holder without a change to the mainboard. In many cases you do not need to drill holes or apply any permanent changes at all.
Alternatively you could mount the battery pack into a plastic container that keeps the goo of some leaking batteries safely in place while leaving the outside appearance of your computer untouched.