There would be but after trying over 10 different ones I couldn't find anything that was reliable. Most of them that had enough juice even charged through the same port as they provided power. So it wasn't convenient enough.
The goal of this case wasn't to go make music on the beach (there's more portable gear for that) but rather visit a friend or do a show at work. So the added power plug is a huge benefit.
Yeah I have battery powered them as wel. But using two powerbanks (because 1 couldn’t deal with 2 devices) inside the case and charging them separately wasn’t appealing to me. So I went with the plug-in one after all.