Instead of plugging in your adapter to electricity, just plug one of these batteries into your pedal and you're ready to do.   

This adapter is great for the Beat Box, Donner, or Ditto guitar pedals (negative center)  Ammoon, or just about any guitar pedal that accepts an external adapter.   Rather than open up an MXR box and put a battery in that will go dead even when youre not using it,  plug this into the adapter socket and take it out when youre not using it, so there is not trickle leakage when its plugged in.   With the cost of 9 volt batteries these days....

This allows you to quickly unplug the battery from the pedal so it won't go dead. 

It can be used for many applications, since is has a very common plug. 

You must find out if you need a negative center or positive center before ordering.  

2.1 internal  5.5 external male connector.

Fits 2.1 mm Standard Female socket.