I've often used a short truck-tarp tie down, the kind that looks like a big black rubber band with S-hooks at each end. On 240's it's possible to pass one end under the rear of the tray and the other over the battery, with the S-hooks joining on the front side of the battery. I make sure the sometimes sharp-edged ends of the S-hooks are not touching the battery casing, since vibration could let them chew. The plastic handle many batteries now come with, if turned to the front, help keep the joined S-hooks clear. Have had one on an '85 for years with no harm. My 740's original clamp is still OK, so I haven't had to try this on that model. I remove batteries for a wash in the basement sink every year or so, then rinse any crud and acid from the empty tray, as well as neutralizing the whole area with a strong soup of baking soda and water. Residue of this soda solution in the tray and elsewhere will continue to neutralize metal-eating acid that invariably creeps down the battery.