# Safely detecting lead-acid battey charger output?

How can I safely detect output of a car battery charger?

It has a OS/MP switch and for output it lists 12 V and 10.1 A. Unfortunately I have no idea what OS/MP means and I of course have no manual. The charger also has a single 5x20 glass slow fuse rated at 2 A and a 10 A standard household circuit breaker.

I'm hoping to use the charger as a power supply for a project. Either constant current or constant voltage would be OK, but I can't determine right now which one the charger is. It looks low-tech, so I doubt that it has both output types.

On the equipment front, I have two multimeters and I could easily obtain various 5 W and 11 W ceramic resistors. I have several 10 $\Omega$ resistors available right now.