Since the Zoom H4n is providing 48V phantom-power two two microphones at once and 7V plugin-power for a lavalier and for any type of recording I can switch between cameras but need one, single, continuous sound-recording.....
The 2 AAA-batteries in the H4n are always dead.
It does have a 230V power-adapter.
In fact, I have two that fit it.
But that's no good on the road.
For my cell-phone I now have this cheap USB-power-supply that I can recharge at any USB-port (and even hand through that power to the real device to charge that too.
Thus only requiring a single USB-port).
As the H4n also runs on 5V, I tried to solder myself a USB-to-H4n adapter and it actually worked!
(GND on the outside, +5V on the center contact)
The nice thing is that the H4n automatically switches between it's batteries and external power.
So now I can even attach USB-power, switch the batteries while drawing USB-power and then run on the fresh batteries when USB-power dies too.