The current crop of affordable rechargable personal speakers are now quite decent sounding.
eg Anker/Soundcore.

They can connect by either bluetooth or line in cable,
and also be powered off adapter plugs while recharging.

Yes, the same kind of speakers gangs of teenagers annoy society with.
But musicias are also finding them convenient to plug an Amp emulation preamp into for practice.
So no reason they couldn't help out with sound reinforcement at sessions.

Worth looking out for deals of the day on Amazon...