Plpenty of bulging and cooked SLA batteries in gate motors, garage doors and alarm systems, anywhere which both run the battery nice and toasty, and then have a constant 14V4 float voltage on them to first of all cause gas generation, which then vents the cells. The liquid generally is caught in the felting in the vent cavity in most cases, and the liquid gradually dries out, and then you get an open circuit battery. If you are unlucky a cell shorts out, and then most chargers cook the remaining ones nicely, so they boil, and then soften the case and cause it to bulge out. Other faults are the terminals rotting off from venting acid eating through the lead terminal seal, and eroding the copper push on blade, and then the wiring attached, and you get the battery with 6 bulges where the cells are. Also got them so dry that they will still read 12V open circuit, just draw 20mA, and see the voltage drop to 1V or less. And those that rattle when shaken.
Then of course the fake ones, where the cells contain 2 lead plates, and the rest of the volume is taken up with a block of recycled polystyrene foam to provide pressure on the plates, to keep the acid gel in contact with the plates. Normally the 7Ah brick should be around 1.2kg, though some that have been cooked nicely, as in 6 split cells in the case, with all of them bulging out and venting white powder, came in at under 1kg.