A good idea but I'll throw out a suggestion for a tad bit of safety: Try to put a 12v headlight bulb or turn signal bulb in series with the battery as you charge the cap. If the cap is good you may get a little flash of light from the lamp. If the cap is shorted then the worst that will happen is the light will stay lit.Connect a 12v battery charger to the cap's terminals, again with appropriate polarity. Observe the voltage rise. Once it has ceased rising, disconnect the battery charger, and observe how voltage drops. If it drops fast, there's an internal leak. If it drops slow, there ain't.
If you try this without the lamp and the cap is shorted then in very short order you'll let the rest of the magic smoke out of it accompanied by a very big BANGand a shower of paper & foil confetti (don't ask). This is know as "peanut buttering" a capacitor........... ...........PD
Editing to add that if the lamp stays lit disconnect it fast or you'll find out what the insides of the capacitor look like..............PD