Ground test 1st when testing using Oscilloscopes

Yes, battery powered will work well, like a multimeter. And, if you don't have a battery scope, you can still connect your regular scope to a computer UPS and make measurements like a pro. However, it's necessary to not touch anything metallic, not even the probe compensation thing.

Besides, if yours is a DSO, the power consumed would usually be only about 20 or 30W, which means the fully charged UPS battery would give you a reasonably long time for measurements before finally running out !