In Canada,
Safety regulations stipulate battery retainer mechanisms are mandatory for mobile equipment.
I once witnessed the aftermath of a forklift that rolled backwards off a dock and landed on its overhead guard upside down, the battery weight was too great for the battery cover and busted the hinges and slammed into the overhead guard, squashing the driver's seat to about 30mm thick and then leaking battery acid over everything.
If the young operator had not jumped clear he would have looked like stawberry jam squashed under that 3000 lb battery.
This concludes my lesson on "Battery Retainers 101".