Another lithium ion battery question

I’m traveling with my daughter-in-law who is prone to headaches and migraines. I bought a temple/eye massager with heat, hoping to take it with us in case she gets a headache while we’re overseas. When it arrived, the outside of the delivery box had a label stating that because of the lithium batteries inside, this device was not to be taken on a passenger airplane. The specs are as follows:

Rated power: 5W

Battery capacity: 1100mAh

The restrictions I’ve read for flying are always listed in terms of what hours, and I don’t know how this translates.