Yeah... I've seen videos where guys are running a Bose Compact off a Duracell 600 battery pack, and they say it will last about 2 hours. That's enough time for a ceremony, but not for a party.
What battery pack do you use, and I wonder how long it might power one of my Alto TS112W Bluetooth speakers? That would make a great ceremony system. It has a mic input.
I thought seriously about one of those Duracell units but the amp-hour rating isn't as high as a straight marine battery/inverter rig. I've often used an EV ZXa1 with wireless, mixer and laptop and it averages a 100-150 watt draw on power. I have no idea how long it would last as I've never tried draining it. As for "what battery pack", as I said, a simple marine (deep cell) battery from walmart. If you need to extend the runtime, just parallel more batteries into the mix. KISS applies.
EverStart Marine Battery, Group Size 27DC - Walmart.com