When you are winching, a lot of stress is placed on all of the components involved.
Check that the eye you are hooking on to is good and able to withstand the loads you are about to impose on it.
At an engine museum meet I was watching a guy loading a Blackstone horizontal engine up some fairly steep ramps when the winch exploded and the engine went backwards rather quickly.
Items falling off ramps are uncontrolled and dangerous, unless you have a very good reason to be there, stay away from ramps when loading/unloading is going on!
We have fitted both our engine trolley drawbars with tow hitches, and a Front Towbar on the Land Rover Discovery, that has eliminated most of the danger points now, we can tow the engines out of the trailer in low box and in complete control.
Regarding batteries and sparks, it is a mixture of Oxygen and Hydrogen that is given off by charging batteries, caused by breakdown of the water in the electrolyte. You shouldn't be gassing the batteries that much in the first place, but I've had an unlucky spark cause the same thing on a battery that had been off charge for some time, but the vent plugs weren't put back in....
Peter