Power bank question: I have a DC 9V 300mHa (not 3000) Zoom H4 Handy recorder I need a power supply for on the go. (Please see details)?

The AA batteries don't last long enough?
I was hoping to use a phone charger power bank but most seem to have upwards of 5000mHa, 10, 12 and 20000mHa and above so don't seem to be suitable.
8 answers 8