Just checked the power consumption there, the Google Home Mini seems to use about 200-300mA while idle and about 400-500mA while playing some loud music. Although I'm only using a USB charger doctor, so the values are all over the place.
So if each of those cells is approx 1500mAh each, I think you'd get roughly about 9 hours of loud music and just over half a day of idling with 3 of them (4500mAh).
That's not really accounting for power losses and what not, so I'd take it with a bag of salt and assume a couple hours less maybe.
Not much of an answer, but I hope it helps some how.