I just wanted something for 5-6 9V pedals that didn't need mains power and I could leave the pedals plugged in so it was quick to set up and pack away. There are a few commercial options available that would do it, but I wasn't sure how long the batteries would last, and I was too tight to try them out.
The short version of the story, for around $60 it works, and my pedals run pretty silently off the power bank for hopefully around 20 hours. (haven't run the battery down yet, so is looking good). To recharge the battery, its just a USB power supply plugged into a USB C connector. But there are a few things to look out for......
There's a thread on thegearpage.net that has some great info about people using power banks, the battery banks you use to charge up your cell phones etc and a step up convertor to bring the voltage to 9V.
So I bought a 15000 mAH Kogan battery bank of trademe (Dick Smith) for $40, a voltage step up convertor off ebay for around $5 and a daisy chain from the rock shop. I thought if it didn't work I could still use the power bank to charge my phone anyway.
The step up convertors all seem to have the connector with the wrong polarity, so you have to swap it around to negative center pin to match most 9V pedals. I also made sure that the power bank had a switch, so it can be turned off while it is still plugged in.
Most power banks have an auto shutoff feature (the one I bought did) so if you're not drawing enough current the thing shuts down after 15 seconds. I found that it did this if I had only one pedal plugged in, but if I had a few plugged in, even if they weren't switched in, I was OK. The other thing that the people on the gear page all talked about was the cct noise from the power banks. It seems to be a bit of a gamble whether it will operate silently depending on the pedals you're running. I found that as long as I had an old Ibanez digital delay plugged in (didn't have to be switched on) everything was pretty quiet. That was running 5 pedals. If I took the delay pedal out, I got a power switching noise that was quite loud, and definitely not acceptable. But if I unplugged the tuner as well, it was quiet again. So still running 2 drives and a tremolo. As I use the delay for slap back sometimes, I kept it in there, and its all good.
Next I put together a board out of an old tea trolley they were throwing out from work, velcroed the battery bank underneath, and bobs yr uncle.
I haven't run it right down so not sure how long it will last before recharging. But in theory, 15000mAh @ 3.7V is 6167 mAh @ 9V minus conversion losses. So if my pedals altogether draw 300mA, hopefully I'll get close to 20 hours out of it.
Here's some pics...
