Very, very rare indeed, so you might reasonably conclude that the weight and stiffness are much more valuable to you in stabilizing your laptop than a tiny, tiny risk of fire from unmodified but dead battery leakage. In my case, I have enough weight from a CDROM drive on the other side and do not move my Pismo much except when wardriving. Also I am not concerned with the cosmetics of the open bay nor dust getting inside. Since I cannot test my recelled charged battery to the same degree as a professional battery remanufacturer I'll continue to distrust it more than an unmodified unit. I'm treating it as an experimental project, not a product to be trusted.

Edited post: I forgot to mention the Laws of Batteries: [] ]'>

1. Household batteries have corrosive stuff inside.

2. A watched battery never leaks.

3. There is an irresistible force between the corrosive stuff and battery contacts (and also nearby circuit boards).

4. The plating on the battery contacts is no match for the corrosive stuff.

5. Most unwatched batteries try to be good, but the worst are the spoiled ones that are stored in your most prized gadget.

6. There are two kinds of unwatched batteries, those that have already leaked, and those that will.