when you say “device”, do you mean a battery pack?
No need to answer that because that specific clarification will not change the answer:
There is no way to know. Every product is different, and they change from batch-to-batch (consider LED light bulbs, where detailed EMI testing reveals that the exact same type of bulbs vary wildly in their EMI emission, depending on exactly when they were manufactured). You would need to test each product in question. That costs about $23,000 last time I paid for it in 2007.
But the real problem is that they would test to federal standards, which would tell you that the device itself meets federal standards, and we all know that federal standards allow a lot of devices that emit hazardous EMI. So this is an easy question to ask but impossible question to answer unless you hire a lab that is willing to develop and run a special test.
You will notice that no one offers the service of testing individual consumer electronics for all forms of potential EMI. That’s because the cost of testing would be 10s of thousands of dollars per device, and typical consumer is not interested in spending $10,000 - $20,000 to know whether or not their toaster or cell phone is really safe, beyond federal standards.
